Laser beam guidance systems and methods

ABSTRACT

An automated adaptive optics and laser projection system is described. The automated adaptive optics and laser projection system includes an adaptive optics system and a compact laser projection system with related laser guidance programming used to correct atmospheric distortion induced on light received by a telescope. Control of the automated adaptive optics and laser projection system is designed in a modular manner in order to facilitate replication of the system to be used with a variety of different telescopes. Related methods are also described.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional ApplicationNo. 61/622,319 filed on Apr. 10, 2012 and incorporated herein byreference in its entirety.

The present application is related to U.S. application Ser. No.13/842,996 entitled “Compact Laser Projection Systems and Methods” filedon even date herewith and incorporated herein by reference in itsentirety. The present application is also related to U.S. applicationSer. No. 13/842,441 entitled “Robotic Adaptive Optics and Laser Systemsand Methods for Correcting Atmospheric Distortion” filed on even dateherewith and incorporated herein by reference in its entirety. Thepresent application is also related to U.S. application Ser. No.13/843,265 entitled “Systems and Methods for Modularized Control ofRobotic Adaptive Optics and Laser Systems” filed on even date herewithand incorporated herein by reference in its entirety.

STATEMENT OF GOVERNMENT GRANT

This invention was made with government support under AST0906060 &AST0960343 awarded by the National Science Foundation. The governmenthas certain rights in the invention

FIELD

The present application is directed to adaptive optics laser systems andrelated devices and software control methods.

BACKGROUND

Images of astronomical objects produced by ground-based telescopes arelimited by degrading effects of turbulent atmosphere. Light from distantobjects arrives at Earth as plane waves. In the absence of atmosphere,the theoretical angular resolution of a telescope is limited only bydiffraction. Such diffraction is measurable by noting the observingwavelength (λ) and dividing the observing wavelength by the size of thetelescope's primary mirror or aperture (D).

However, in reality, one must account for atmosphere. The atmospherecontains cells of air at different temperatures with resulting differentindices of refraction. The presence of such atmosphere causes the lightto become non-planar. This causes the ground-based telescopes, when theytry to focus on these light waves, to obtain images which appeardistorted and blurry. Such images also change as a function of time asthe atmosphere the light waves travel through also change over time.

In order to compensate for distortions caused by the atmosphere, laseradaptive optics systems have been used. Such systems are capable ofmeasuring the atmospheric distortions induced onto a laser projectedinto the sky and then apply compensating effects accordingly to thelight received by the ground-based telescope since the light would havesimilar distortions as the laser.

Laser adaptive optics systems can compensate for effects of atmosphericturbulence. A high-powered laser is projected in the direction thetelescope is pointed and is used as a probe of the atmosphere. A tinyfraction of the laser light from the high-power laser returns backtowards the telescope which has similar non-planar optical distortionsas the light being observed. Internal measurements and calculations doneby the laser adaptive optics system on the shape of the laser lightreceived can then be used to shape the incoming light waves beingobserved to be flat (planar) again.

SUMMARY

According to a first aspect of the present disclosure a systemcomprising: a laser projection system configured to project a laserbeam, whereby at least a portion of the laser beam is returned to thesystem for detection of an error; an adaptive optics system configuredto use the detected error to perform a compensating action comprisingmodifying an operating characteristic of at least one optical componentcontained in the laser projection system; and an automated laseralignment system comprising a computer, the computer including aprocessor and a computer-readable storage medium, the computer-readablestorage medium having stored thereon, instructions for automaticallyperforming steps directed at a) controlling the projection of the laserbeam by the laser projection system and b) executing the compensatingaction in the adaptive optics system.

According to a second aspect of the present disclosure a methodcomprising: activating a laser projection system to propagate a laserbeam, whereby at least a portion of the laser beam is returned to thesystem for detection of an error; configuring an adaptive optics systemto detect the detected error to perform a compensating action comprisingmodifying an operating characteristic of at least one optical componentcontained in the laser projection system; and executing acomputer-controlled automated acquisition procedure to automaticallyalign the laser projection system, the automated acquisition procedurecomprising: capturing in a wavefront sensor, an image associated with aportion of the projected laser beam returned; and using informationobtained by processing the captured image to perform a compensatingoperation directed at addressing the error.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top schematic view showing a robotic adaptive optics lasersystem with a telescope in accordance with the present disclosure.

FIGS. 2A-C show a compact laser projection system used in the roboticadaptive optics laser system of FIG. 1.

FIGS. 3A-B show in more detail internal components and light paths ofthe adaptive optics system. In particular, FIG. 3A shows the internalcomponents and light paths of the adaptive optics system. FIG. 3B showsthe internal components and light paths of the internal light sourceused during a calibration mode of the adaptive optics system.

FIG. 4 shows an adapter bracket used to attach the compact laserprojection system to the telescope.

FIG. 5 shows the compact laser projection system being attached to thetelescope via the adapter bracket.

FIG. 6 shows a system adapted for naked-eye observation whereby avisible light path within the adaptive optics system is reflected to aneyepiece through the use of a beam splitter.

FIG. 7 shows an architectural layout of the control software used in thesystem according to the disclosure.

FIG. 8 shows a high level flow chart for one of the subsystem daemonsused in the system of the disclosure. In particular, FIG. 8 shows a flowchart for a weather monitoring control subsystem daemon.

FIG. 9 shows a software architecture of a telescope status controlsubsystem daemon.

FIG. 10 shows a software architecture of a telescope control systemcontrol subsystem daemon.

FIG. 11 shows a software architecture of an atmospheric dispersioncorrector control subsystem daemon.

FIGS. 12-1 and 12-2 show a software architecture of a ‘visibleinstrument camera’ control subsystem daemon.

FIGS. 13-1 and 13-2 show a software architecture of an infrared cameracontrol subsystem daemon.

FIGS. 14-1 and 14-2 show a software architecture of an adaptive opticscontrol subsystem daemon.

FIGS. 15-1 and 15-2 show a software architecture of a laser guide starcontrol subsystem daemon.

FIGS. 16-1 and 16-2 show a basic architecture of a robotic controlsystem subsystem daemon.

FIGS. 17-1 and 17-2 show a detailed flow chart of a robotic systemcontrol observation thread.

FIG. 18 shows a flow chart for an operation of a laser beam guidancesystem.

FIG. 19 shows a computer system that may be used to implement therobotic adaptive optics laser system of the present invention

DETAILED DESCRIPTION

Embodiments of the present disclosure aim to fully automatizecalibration and operation of a telescope, e.g. a ground based robotictelescope, with its adaptive optics and laser projection system. This isachieved in two ways: 1) modularization within the adaptive optics andlaser projection systems so that the adaptive optics and laser systemscan easily be replicated and customized for any telescope and 2)implementation of corresponding software to automate the entire process,the software being implemented in a way that facilitates themodularization of the adaptive optics and laser projection system. Thedetailed description of the present application will first describe indetail the apparatus and hardware pertaining to the robotic adaptiveoptics laser system (Robo-AO). Afterwards, a detailed explanation of thecorresponding software and methods used to operate the Robo-AO will beprovided.

Hardware/Apparatus

FIG. 1 is a top schematic view showing a robotic adaptive optics laser(Robo-AO) system (2, 3, 4) being associated with a telescope (1). TheRobo-AO system includes a container mounted at a focus of the telescopethat houses an adaptive optics (AO) system and respective scienceinstruments (2), a set of support electronics and computers (3) and acompact laser projection system (4).

The set of support electronics and computers (3) includes at least oneprocessor used to oversee the entire Robo-AO system. It will beunderstood that the word “processor” as used herein in this disclosure,can be interpreted in some embodiments as referring to a single device(such as a microprocessor chip), and in other embodiments as referringto a computer unit containing multiple elements (such as a controllerdevice incorporating a microprocessor chip and input-output circuits).Such variations in terminology will be understood in the context ofusage, by persons of ordinary skill in the art.

Additionally, the compact laser projection system (4) of the Robo-AOprovides a laser beam (5) used to measure (or probe) for opticaldistortions caused by atmospheric turbulence which would be induced ontoobserved light that the telescope (1) would receive from an object to beobserved (such as an astronomical object in the sky).

Although FIG. 1 and the related text of the present application describeembodiments using a telescope, the person skilled in the art willunderstand that the present application is also applicable in otherembodiments. The benefit of using the Robo-AO with respect to atelescope is to provide a process of acquiring images from objects to beobserved in a more efficient manner as well as without the use of ahuman operator.

Without the use of the AO system (2), images obtained by the telescope(1) are distorted and unclear. Such distortion and clarity issues withthe images are caused by atmospheric turbulence induced on the lighttraveling from the target or object to be observed (e.g., anastronomical object) to the telescope (1). Calibrations to the telescope(1) and accompanying systems are provided to compensate for the givenpresence of atmospheric turbulence. A general description of the processis provided below.

After the telescope (1) is pointed at a selected object to be observed,a compact laser projection system (4) is turned on. The compact laserprojection system (4) emits a laser beam (5) in the same direction asthe robotic telescope (1) towards the selected object.

A wavefront sensor (not shown in the figure) within the AO system (2)obtains Rayleigh scattered light from the laser beam (5) returning backfrom the atmosphere from around ten kilometers away. The reflected laserbeam (5) is used to measure a dynamic wavefront error induced by theatmosphere. A control computer within the set of support electronics andcomputers (3) calculates a compensatory shape for a deformable mirror(42) within the AO system (2) to correct for the measured dynamicwavefront error obtained. The AO system (2) then applies the correctionto the incoming light from the object being observed by the telescope(1). This correction is possible because the Rayleigh scattered lightfrom the laser beam (5) should contain similar non-planar opticaldistortions caused by the atmosphere as the light from the object beingobserved.

The control computer described above sends commands and receivesfeedback from the telescope (1) and the AO system (2). The same controlcomputer also commands other support electronics (2) used to control asub set of components of the AO system (2) and the compact laserprojection system (4).

Focus will now turn to the compact laser projection system (4) used inthe Robo-AO system as seen in FIGS. 2A-2C. The compact laser projectionsystem (4) includes a high-powered laser source (6), a redundantexternal safety shutter (7), a half-wave plate (8), a beam steeringmirror (9) and a positive lens (10). The control computer describedabove is capable of controlling all the above elements (6, 7, 8, 9 and10) within the compact laser projection system (4).

Generally observatories have laser projection systems which are muchlarger and cannot be attached to the side of the ground-based telescope.These laser projection systems can have multiple parts (e.g. the lasermay be physically separate from the projection optics), may be housed inseparate rooms and custom built for a particular or specific type oftelescope. The concept of miniaturizing and standardizing a laserprojection system to be used across a plurality of different types oftelescopes has not been previously undertaken, and will be described indetail below. The outcome in accordance with the present disclosure isthat a single laser projection system can be easily replicated to beused over a number of different telescopes.

The embodiments of FIGS. 2A-2C of the present disclosure describe acompact laser projection system (4) which is not only compact but alsomodular in design. This facilitates replication and use of such laserprojection system among numerous different ground-based telescopes. Withthe exception of the drive electronics and laser chiller which can beten or more meters away, all the elements associated with the compactlaser projection system (4) is contained in a housing element (which is,for example, 1.5 m long, 0.25 m high and 0.5 m wide). The housingelement can be attached and detached from a telescope. The housing (e.g.a box) is, for example, approximately 70 kg in weight. Such compactpackage, compared to prior implementations of the laser projectionsystem, makes the present design of the compact laser projection system(4) easier to replicate. Furthermore, attachment platforms or adaptorbrackets (later described below) are provided so that the compact laserprojection system (4) can be attached to several different types oftelescopes.

With reference to FIG. 2A, a cross-sectional view from the top of thecompact laser projection system (4) is provided. This view illustratescomponents as well as an internal arrangement of the compact laserprojection system (4). The compact laser projection system (4) containsa high-powered laser source (6), a redundant external safety shutter(7), a half-wave plate (8), a moveable beam steering mirror (9),positive lens (10) and a fold mirror (11). All the above elements of thecompact laser projection system (4) are mounted on a lightweight andstiff honeycomb breadboard (14). The compact laser projection system (4)also contains an output aperture and lens (12) connected to the stiffhoneycomb breadboard (14) by two substantially perpendicular lightweighted cantilever lens mounts (16).

The output aperture and lens (12) are not directly connected to theexternal enclosure of the compact laser projection system (4). Instead,the output aperture and lens (12) are mounted at a free-standing end ofthe cantilever lens mount (16) that is projected beyond the honeycombbreadboard (14). The cantilever lens mount (16) has the other endattached to the honeycomb bread board (14).

With respect to the high-powered laser source (6), the laser source isused to generate a laser beam for the compact laser projection system(4) to be used. By way of example, the high-powered laser source (6) iscapable of firing a 10 W beam. The beam diameter and divergence is notcritical and can be changed via the positive lens (10). The wavelengthof the high-powered laser source (6) is between 340 nm and 390 nm.Typical commercial wavelengths for laser sources can be between 351 nmand 355 nm. Additionally, by way of example, pulse laser length can bebelow 100 ns. In several embodiments, the laser pulse repetition rate isdesired to be at least 1.2 kHz to operate the AO control system. Such arate corresponds to one pulse per measurement. At most, the laserrepetition rate should be 15 kHz to avoid having more than one returninglaser beam in the atmosphere at the same time.

Reference is now made to the redundant external safety shutter (7) ofFIG. 2A. The redundant external safety shutter (7) is provided as anextra layer of safety. Although these shutters have been included in theembodiment shown in FIG. 2A, there may be embodiments which do notutilize them. This is possible because the high-powered laser source (6)has its own internal shutter.

Next, focus will be placed on the half-wave plate (8). The half-waveplate (8) is located inside a motorized rotatable stage which is used bythe compact laser projection system (4) to rotate the linearpolarization of the projected laser beam corresponding to the beam oflaser light (5) of FIG. 1. By rotating the half-wave plate (8), thepolarization of the linearly polarized light source can be rotated. Themagnitude by which the polarization can be rotated is twice an angle ofrotation of the half-wave plate (8).

The above application of the half-wave plate (8) is significant becausethe first and second linear polarizers (60, 62) and the Pockels cell(61) of the AO system (2) (as seen in FIG. 3 below) desire laser lightpolarization orientation to be in a particular direction. The aboveprocess of Rayleigh scattering of the laser light preserves a particularpolarization. Therefore, a matching arrangement to match thepolarization produced by the compact laser projection system (4) tomatch the polarization needed by the first and second linear polarizers(60, 62) is desired.

In alternative embodiments, the half-wave plate (8) could be omitted ifthe AO system (2) were rotated with respect to an optical axis of thetelescope. Rotating the AO system (2) in such a way would match thepolarization of the returning laser beam and the first and second linearpolarizers (60, 62). Alternatively, one could engineer a mount for theAO system (2) to provide a proper orientation.

Rotation of the half-wave plate (8) is performed through a motorizedrotation stage to which the half-wave plate (8) is mounted to. Themotorized rotation stage is used so that the half-wave plate (8) can berotated without opening the housing of the compact laser projectionsystem (4). Once a proper orientation is found for a given telescope andAO system setup, the position of the half-wave plate (8) usually doesnot need to be changed unless the same laser projector (4) is used indifferent telescope setups. However, there may be situations where, forexample, an instrument field de-rotator is used with an Alt-Az typetelescope, motorization of the half-wave plate may be necessary.

The next element in the compact laser projection system (4) is themoveable beam steering mirror (9). The moveable beam steering mirror (9)operates to reposition the laser beam from the high-powered laser source(6), thereby repointing the laser beam (5) being projected out of thecompact laser projection system (4). The moveable beam steering mirror(9) is optically conjugated to the output aperture and lens (12). Inother words, the positive lens (10) creates an image of the moveablebeam steering mirror (9) at the same physical location as the outputaperture and lens (12). Additionally, the positive lens (10) also cancreate an image of the output aperture and lens (12) at the samephysical location as the moveable beam steering mirror (9).

Because of the relationship between the moveable beam steering mirror(9) and the output aperture and lens (12), the laser beam from thehigh-powered laser source (6) does not shift at the output aperture andlens (12) as the moveable beam steering mirror (9) is tilted indifferent directions. Additionally, such arrangement allows the laserbeam from the high-powered laser source (6) to pivot about the outputaperture and lens (12).

As discussed later, the moveable beam steering mirror (9) is controlledby wavefront sensor using tip and tilt signals. When commanded by thewavefront sensor, the moveable beam steering mirror (9) executes anoutward spiral pointing procedure.

According to an embodiment of the disclosure, the moveable beam steeringmirror (9) can repoint the laser beam (5) at rates of several hundredsHertz and over a total useable range of 160 by 228 arcseconds. Inparticular, there may be situations where the telescope (1) readjustsits direction and angle to acquire a target. In such situations, themoveable beam steering mirror (9) is able to repoint the laser beam (5)in order to realign the laser along the same optical axis as thetelescope (1). Modes of operation pertaining to how the compact laserprojection system (4) compensates for changes in the direction and angleof the telescope (1) will be further described below with reference tothe software and methods used to control the compact laser projectionsystem (4).

The total usable range (e.g. 160 by 228 arcseconds) is determined by howparallel the optical axis of the telescope and the optical axis of thecompact laser projection system (4) can be maintained as the telescopepoints to different areas, as the overall system may experiencedifferent gravity vectors. Additionally, individual mechanicalstructures of the telescope as well as the rigidity of the telescope mayalso influence the total usable range.

With respect to the update rates (e.g. several hundred Hz) by which themoveable beam steering mirror (9) can repoint the laser beam (5), aslower update rate will tend to increase the amount of time it takes thesystem to find the laser beam (5). Generally, the update rate should befast enough (e.g. 100 Hz) in order to keep up with vibrations in thetelescope (1) and the compact laser projection system (4) structure sothat accurate corrections can be made.

With continued reference to FIG. 2A, the laser beam from thehigh-powered laser source (6) then encounters the positive lens (10).The positive lens (10) is on a motorized positioning stage and is usedto refocus the laser beam (thereby creating a beam waist) as discussedabove.

With reference to the beam waist, situations may arise with prior artdesigns where the creation of intermediate foci of the laser beam withvery high fluence levels can ionize air and disrupt propagation of thelaser beam. This occurs because a mixture of super-heated gas and plasmais created at the beam waist thereby creating a chaotic lens in the air(turbulence) which would affect the laser beam passing through it. Suchan occurrence tends to reduce overall transmission and results in a muchlarger projected laser spot, such as, e.g. a projected laser spot on thesky. The larger spot could negatively impact the performance of the AOsystem and could potentially prevent the AO system from working.However, such problem is not present in the structure according to thepresent disclosure, as such structure does not contain fluence levelshigh enough to ionize the surrounding air within the laser projectionsystem.

A benefit of using the positive lens (10) instead of an alternativenegative lens is that the moveable beam steering mirror (9) and theoutput aperture and lens (12) can be made optically conjugated asdiscussed above. This prevents the laser beam from the high-poweredlaser source (6) from shifting at the output aperture and lens (12) asthe moveable beam steering mirror (9) is tilted in different directions.Therefore, one can maintain maximum throughput of the laser beam throughthe output aperture and lens (12).

If the positive lens (10) is not used and a negative lens is usedinstead, the effect would be that the moveable beam steering mirror (9)and the output aperture and lens (12) would not be optically conjugate.This would result in an outcome where the moveable beam steering mirror(9) is moved to different angles (such as in processes for re-acquiringthe laser beam) and the laser beam from the high-powered laser source(6) would wander on the output lens (12) resulting in a transmissionloss. Therefore, although use of a lens that is not a positive lens ispossible, doing so will result at a cost of reduced performance.

An additional feature of the positive lens (10) is now described. Bymoving the positive lens (10) forwards and backwards, an image of thelaser waist can be projected over a range of several kilometers. Thedistance from the positive lens (10) to a reimaged beam waist is afunction of the forward and backward movement of the positive lens (10).Therefore, by moving the positive lens (10), one can move the locationof the beam waist with respect to the output lens (12) (corresponding tothe laser beam (5) being projected out of the compact laser projectionsystem (4)).

By nature of a location of the beam waist being near the front focaldistance of the output aperture and lens (12), a small change in theforward or backward motion of the positive lens (10) can cause verylarge changes in the distance the laser beam (5) is ultimately focused.For example, by moving the positive lens (10) thereby extending thereimaged beam waist by about 50 μm, the laser beam focus distance on thesky can be changed by 2 km.

The compact laser projection system (4) also uses the fold mirror (11)for the purpose of redirecting the laser beam from the positive lens(10) to the output aperture and lens (12). The fold mirror (11) isstationary and mounted to the honeycomb breadboard (14). The fold mirror(11) folds an optical path of the laser beam to keep the compact laserprojection system (4) more compact compared to situations where the foldmirror (11) is not used. Therefore, the fold mirror (11) can be omittedif compactness of the laser projector box is not an issue.

The laser beam from the high-powered laser source (6) travels throughthe output aperture and lens (12) to create an almost collimated beam,corresponding to the laser beam (5) of FIG. 1. As stated above, therelationship of the positive lens (10) and the output aperture lens (12)influences the image of the beam waist (and the distance the laser beam(5) is projected) out of the compact laser projection system (4).According to an embodiment of the present application, an image of thebeam waist corresponding to a distance of 10 km is used, although largeror shorter distances (e.g. 12 km and 6 km respectively) are alsopossible. Alternative distances from the image of the beam waist canalso be implemented by changing a radius of curvature and conic constanton the powered side of the output lens (12).

The above elements, in particular the high-powered laser source (6),moveable beam steering mirror (9), positive lens (10), output apertureand lens (12) and fold mirror (11) all form a compact loopbackarrangement. Such compact loopback arrangement assists in and providesthe compact laser projection system (4) with the “miniaturization” orcompactness features. Details will now be provided below regarding thenon-optical elements of the compact laser projection system (4).

The high powered laser source (6), the redundant external safety shutter(7), the half-wave plate (8), the moveable beam steering mirror (9), thepositive lens (10) and the fold mirror (11) are all mounted on alightweight and stiff honeycomb breadboard (14). As shown in thecross-sectional side view of FIG. 2B, the use of the stiff honeycombbreadboard (14) provides an improved alignment for all optical elementsof the compact laser projection system (4).

Although stiff alignment is also desired for the output aperture andlens (12), the output aperture and lens (12) are not directly connectedto the honeycomb breadboard (14) because such a connection would blockpart of the expanding laser beam. To overcome the problem, the outputaperture and lens (12) is connected to the honeycomb breadboard (14)through two perpendicular and substantially light-weighted cantileverlens mounts (16) as described above.

Additionally, the output aperture and lens (12) is not directlyconnected to the external enclosure of the compact laser projectionsystem (4). Rather, a small gap is provided, for example around 1.5 mmwide, which is filled by a compliant gasket material. Such small gapmechanically decouples the above referenced optical elements (e.g. thehigh-powered laser source, the moveable beam steering mirror, etc. . . .) from the external enclosure of the housing. This is significantbecause the external enclosure can shift and flex under its own weightinfluenced by different gravity vectors. The above referencedarrangement with the honeycomb bread board (14) allows the externalenclosure to shift and flex without affecting any of the opticalelements inside the compact laser projection system (4) mounted to thehoneycomb breadboard (14).

The gap itself is filled to keep the enclosure of the compact laserprojection system (4) sealed against dust and other particles which mayenter the system and provide interference. The use of a compliant gasketmaterial to seal the gap maintains the seal with negligible contactforce between the enclosure and the output aperture and lens (12) and isable to adapt as the gap changes size over different gravity vectors.

As stated above, FIG. 2B shows a cross-sectional view of the compactlaser projection system (4) of FIG. 2A. In particular, the honeycombbreadboard (14) is shown mounted to two crosswise mounted ribs (15). Thetwo crosswise mounted ribs (15) have attachment points (15.5, two whichare shown and two which are hidden by the positioning of thehigh-powered laser source (6)) to the honeycomb breadboard (14) and abase of the enclosure (17) of the compact laser projection system (4).The above configuration keeps the attachment points (15.5) in very closeproximity (e.g. 3 inches) to the mounting points (18) of a laserprojector adaptor later described below. In general, by minimizing adistance between the attachment points (15.5), a pointing stability ofthe honeycomb breadboard can be tied more directly to the laserprojector adaptor (later described).

As stated above, all of the optical elements of the compact laserprojection system (4) are connected to the honeycomb breadboard (14) inone manner and are therefore mechanically decoupled from the externalenclosure (17) of the compact laser projection system (4). This allowsthe compact laser projection system (4) to be used over a full range ofangles. In particular, as different angles are used, changing gravityvectors induce mechanical sag to the external enclosure (17). Suchmechanical sag could then directly affect the optical elements if theoptical elements were attached to the external enclosure (17). However,because the honeycomb breadboard (14) is decoupled from the externalenclosure (17), the mechanical sag of the external enclosure (17) causedby changing gravity vectors does not affect the optical elements. Thisarrangement improves alignment of all optical elements within thecompact laser projection system (4) over the range of angles used.

FIG. 2C shows electrical connections to components within the compactlaser projection system (4). As shown in the figure, all the electricalconnections to components within the compact laser projection system (4)go through an electrical interface panel (13). The electrical interfacepanel (13) is a removable panel that is on the side of and is attachedto the laser projection system (4) as seen in FIG. 2A.

The redundant external safety shutter (7) uses shutter connection(13.1). A temperature sensor is attached inside via temperatureconnection (13.2). The high powered laser (6) uses ground connection(13.3) for ground, laser connection (13.4) for power and control andtrigger connection (13.5) for a laser trigger. AC power for an internalheater is supplied through power connection (13.6). A focus stage forthe positive lens (10) is controlled through focus connection (13.7).Additionally, the beam steering mirror (9) is controlled through mirrorconnection (13.8). Although not directly part of the electricalinterface panel (13), two plumbing connections (13.9) provide liquidcooling to the high powered laser (6).

As stated above, the compact laser projection system (4) operates byproviding a probe for the AO system (2) so that the AO system (2),described in detail next, can determine an atmospheric distortion andapply a correction or compensation to the light coming from a desiredobject to be observed because such light from the object and light fromthe returned laser beam contains similar atmospheric distortions.

Reference will now be made to FIG. 3A, which shows in detail internalcomponents and light paths of the AO system (2) enclosed in a containeror casing mounted at a focus of the telescope (1), as previously shownwith reference to FIG. 1. The AO system (2) is used to compensate foratmospheric distortion on the observed light by measuring the distortionobserved in the returned laser beam (5) and applying a correction to theobserved light from the desired target (e.g. an astronomical object).Typically, the AO system (2) takes thousands of measurements per secondalthough more or less can be taken, as long as a sufficient number ofmeasurements are taken in order to constantly and accurately compensatefor the atmospheric distortion being induced onto light coming from theobserved object.

In the embodiment shown in FIG. 3A, all the components described belowcan be attached to a light weight plate (39) on a three-point mount (toavoid deforming the plate) which attaches directly to the telescope (1).

During operation of the telescope (1) and the compact laser projectionsystem (4), light enters the AO system (2) through a small aperture (notshown) in the center of the light weight plate (39). The light enteringthe AO system (2) includes light both from the selected object to beobserved (e.g. astronomical objects) as well as Rayleigh scattered lightfrom the laser beam (5) coming from the compact laser projection system(4) combined by the telescope (1).

The light entering the AO system (2) is then reflected by a fold mirror(40) with an ultraviolet (UV)-enhanced silver coating on a retractablestage. The fold mirror (40) is used to direct the light from thetelescope into the AO system (2). Without the use of the fold mirror(40), the light would just pass through the AO system. The fold mirror(40) changes the light's direction from being perpendicular to beingparallel with reference to the light weight plate (39) of the AO system(2). As stated above with reference to the fold mirror in the compactlaser projection system (4), the fold mirror (40) in the AO system (2)can likewise be removed in alternative embodiments. However, since thefold mirror (40) here is being used to assist in the packaging of the AOsystem (2), implementation of the AO system (2) without the fold mirror(40) would potentially increase an area the AO system (2) would take up.

The fold mirror (40) of the AO system uses a silver coating becausesilver is a superior reflecting material for optical and near infraredwavelengths which are the wavelengths which the AO system according tothe present disclosure typically observes at. However, since silver is apoor reflector of UV light, a UV enhanced coating is also provided, toextend the reflectivity down to UV wavelengths. Alternatively aluminumcould be used as a replacement, but this would result in a loss of about10% in reflectivity per surface.

Alternatively, the fold mirror (40) can be retracted via its motorizedlinear stage. Instead of directing the light from the telescope (1) intothe AO system (2), the fold mirror (40) reveals light from an internallight source which optically mimics on-sky operation with a black bodyoptically conjugate to infinity and a UV source at 10 km to mimic thelaser.

Reference is now made to FIG. 3B which shows internal components andlight paths of the internal light source within the AO system (2). Suchinternal light source and arrangement is utilized to calibrate the AOsystem (2) when the telescope (1) and compact laser projection system(4) are not being operated. The calibration provides the AO system (2)with calibration sources that mimic the light sources that would be seenthrough the telescope (1) without any (or minimal) optical aberration.In particular, the arrangement of FIG. 3B is used to 1) opticallycalibrate the deformable mirror (42) to null out any alignment errors inthe visible light (53) and infrared camera (66) light path and 2)optically calibrate the non-common path errors that may exist betweenthe optical paths of the visible light (53) and infrared (66) camerasand the wavefront sensor.

With continued reference to FIG. 3B, the arrangement has a blackbodypoint-source radiator (70) that is optically conjugate to infinity,having the same f-ratio and exit pupil position as a star would have ifit was imaged by the telescope (1). In an example embodiment, theblackbody point-source radiator (70) can be an incandescent lamp with aport to attach an optical fiber (71).

Visible and near-infrared light produced by the blackbody point-sourceradiator (70) travels down the optical fiber (71) until it exits theoptical fiber (71). A fiber mount is provided at the end the opticalfiber (71). In an alternative embodiment, the blackbody point-sourceradiator (70) may be a laser diode with a fiber output connected to asingle mode fiber adapted to the wavelength of the laser diode.

A 1 μm pinhole (72) is affixed to the end of the fiber tip therebyreducing the effective size of the point source from the radiator fromabout 5 μm to about 1 μm. The pinhole (72) also significantly reducesthroughput. In an alternative embodiment, the 1 1 μm pinhole (72) couldbe fed by a microscope objective with greater optical throughput thanthe optical fiber (71) and blackbody point-source radiator (70).However, this alternative takes up more physical space.

As the light from the blackbody point-source radiator (70) leaves eitherthe fiber end or the pinhole (72), the light passes into a 50/50 opticalbeam splitter cube (73). Half of the light is reflected off of theinternal surface of the beam splitter and propagates to a sphericalmirror (74). The spherical mirror (74) then collimates the light whichthen passes through the beam splitter cube (73) again to a simulatorstop (75).

The simulator stop (75) defines a pupil size of the simulator, whichultimately defines the final reimaged f-ratio. As the light continues topropagate, it passes through a second beam splitter cube (76) and to asecond spherical mirror (77). The second spherical mirror (77) focusesthe light in reflection which passes back through the second beamsplitter cube (76). With the second beam splitter cube (76), half of thelight is reflected off of an internal surface and comes to a focus at apoint (78).

The second part of the calibration system uses a UV light source (79).The UV light source (79) can be either a UV light emitting diode or alow power UV laser. In either case, only a few mW of total power is usedfrom the UV light source (79).

The UV light source (79) is coupled to a 100 μm core diameter multi-modefiber connected to a fixed fiber end holder. When reimaged, thisapproximates the size of the Rayleigh scattered laser beam as seen bythe telescope (1). Light exiting from the fiber tip is expanding and isthen almost collimated by a lens (81). This light then propagates to thebeam splitter cube (73) where the light reflects off of the internalsurface towards the simulator stop (75).

The UV light is then forced to have the same footprint as the light fromthe blackbody point-source radiator (70). This is achieved by having theUV light propagate through the second beam splitter cube (76) and to thesecond spherical mirror (77) like with the light from the blackbodypoint-source radiator (70). The second spherical mirror (77) focuses theUV light in a reflection which passes back through the second beamsplitter cube (76). The second beam splitter cube (76) reflects roughlyhalf off of the internal surface. This UV light then comes to a focus ata second point (82). The two points (78, 82) are used to calibrate theAO system.

When the fold mirror (40) (seen in FIG. 3A) is in the way of the lightcoming from the telescope (1), the fold mirror (40) of the AO system (2)intercepts the light and directs it to the first off-axis parabolicmirror (41). When the fold mirror (40) is moved out of the way, the twofocus points of the blackbody point-source radiator and UV light (78 and82) coincide with the same points in space as the focus of a star and ofthe 10 km UV laser focus respectively (while also matching the f-ratioand exit pupil of the telescope).

Returning to FIG. 3A, for the situation where the internal light sourceis not used (and the fold mirror (40) is in the position to interceptthe light coming from the telescope (1)), the light entering the AOsystem (2) then passes to an off-axis parabolic mirror (41) which imagesthe pupil of the telescope onto a deformable mirror (42). The off-axisparabolic mirror (41) also has a UV-enhanced silver coating. Thepositioning of the off-axis parabolic mirror (41) is provided in orderto minimize aberrations while simultaneously reflecting the light off atan angle. If the light was to be reflected back on itself, the lightwould not be as useful because subsequent optical elements would blockthe light.

The deformable mirror (42) is an active optical component which is usedto apply spatially resolved phase delays in reflection across a lightbeam that is incident upon the surface of the deformable mirror (42).The application of the spatially resolved phase delays is providedthrough the use of a grid of small actuators, which can push and pull areflective face sheet of the deformable mirror (42).

The deformable mirror is controlled via a USB connection from thecontrol computer in the box that contains other support electronics (3).Furthermore, the shape of the reflective surface of the deformablemirror can be updated at a rate of over 3000 Hz. Practically, thedeformable mirror (42) is updated after a measurement is made with thewavefront sensor and a new shape is calculated by the control computer.

The deformable mirror (42) is typically located in a position that isoptically conjugate to the pupil of the telescope (1). Such a positionalso corresponds to the image of the primary mirror of the telescope(1). This location is significant because it represents the locationwhere the footprint from the returning laser beam (5) and the light fromthe object being viewed exactly overlap.

The deformable mirror (42) uses a low-refractive-index material coatedwith an anti-reflection coating to protect the mirror from humidity. Anexample of an applicable low-refractive-index material that can be usedis magnesium fluoride (MgF₂). Alternatively, CaF₂ and BaF₂ could also beused but may have problems with humidity. Additionally, the deformablemirror (42) could be replaced with other glasses, with or withoutanti-reflection coatings at the cost of decreased optical transmission.

The low-refractive-index material coated with the anti-reflectioncoating can operate from a wavelength of 350 nm to 2200 nm. The lowerwavelength end allows maintaining high transmission for returning UVlaser light. On the other hand, the upper wavelength end covers themaximum range of scientific light that is expected to be imaged by thescience cameras (e.g. visible light camera (53)).

Alternatively, it is possible to utilize coatings which provide anarrower range. For example, if a system is only desired to work invisible light, a coating operating from 350 nm to 1000 nm is sufficient.Such a range is a typical of the long wavelength cutoff forsilicon-based detectors like CCDs or CMOS.

With continued reference to FIG. 3A, after reflection from thedeformable mirror (42), an UV dichroic (43) reflects light with awavelength under 390 nm, corresponding to UV light, to a condenser lens(55) and transmits light with a wavelength over 390 nm, corresponding tovisible and near-infrared light, to an off-axis parabolic mirror coatedwith protected silver (44).

The UV dichroic (43), as stated above, splits the UV light from thevisible and infrared light. The location of the UV dichroic (43) isrelevant, as the light of the observed object (e.g., starlight) comingfrom the off-axis parabolic mirror (41) is perfectly collimated with noadditional optical error while the light from the returned laser beam isstill diverging and can pick up significant amount of coma opticalaberration. The above stated deformable mirror (42) is effectively aflat surface so it does not cause any additional issues with either thelight sources (from the observed object or the laser beam). On the otherhand, the UV dichroic (43) should be in the path of the laser beam (5)so that the wavefront sensor can measure the optical errors caused bythe atmospheric turbulence after the deformable mirror (42) hasattempted to correct the errors.

By placing the UV dichroic (43) immediately after the deformable mirror(42), the deformable mirror (42) is in the path of the laser beam and noother optics have to deal with objects at different distances (whichcould cause additional optical errors in one or both of the lightpaths).

With respect to the visible and near-infrared light, a second off-axisparabolic mirror (44) coated with protected silver refocuses the visibleand near-infrared light to an intermediate focus before it isre-collimated by another off-axis parabolic mirror (45) coated withprotected silver.

In accordance with an embodiment of the present disclosure, there aretwo optical relays between a focus of the telescope (1) and the imageplane of scientific cameras (e.g. the visible light camera (53) andinfrared camera (66)) in the AO system (2). Each optical relay includesa first off-axis parabolic mirror which collimates the light and asecond which refocuses it. Normally, having two relays is avoided ifpossible because the two relays could create extra reflections therebyreducing overall throughput. However, the implementation of thedeformable mirror (42) is small enough that it would be harder toinclude all the functionalities of the dispersion corrector (47), faststeering mirror (48), visible dichroic mirror (50), visible light filterwheels (52) and the eyepiece (93) all into a single optical relay.Therefore, two relays are used in such embodiment, although embodimentswhich use more or less than two relays are also possible.

Next, a fixed fold mirror (46) directs the visible and near-infraredlight to an atmospheric dispersion corrector (ADC) (47) located at areimaged pupil of the telescope. The ADC (47) comprises two motorizedrotating prisms. The ADC (47) works independently of the AO system (2).However, the ADC (47) is used because it solves an issue relating toobserving objects through the atmosphere that are not directly overhead.

In particular, the atmosphere acts as a prism and refracts light as afunction of wavelength. As the telescope points lower in images, theoverall effect of the refraction becomes stronger. This causes theimages to appear elongated in a direction normal to the horizon,especially those images which have been sharpened by AO systemcorrections. The ADC (47) can add an opposite amount of dispersion tothe incoming light which effectively negates the effect of the prismaticdispersion caused by the atmosphere.

While other embodiments may not place the ADC (47) at the reimaged pupilof the telescope, doing so minimizes the size of the prisms used by theADC. This is due to the fact that all the light received by thetelescope (1) passes through a very well defined aperture at thereimaged pupil.

Alternatively, there may be situations where the ADC (47) is notbeneficial. In particular, such situations arise if objects are viewedthat are close to and directly overhead (within ˜20 degrees) of thetelescope (1). Additionally, the ADC (47) may not be used if narrowbandscientific filters are used in front of the visible light (53) orinfrared cameras (66).

After the visible and near-infrared light passes through the ADC (47), afast steering mirror (48) reflects the visible and near-infrared lightto a third off-axis parabolic mirror coated in protected silver (49)which refocuses the visible and near-infrared light one more time. Thefast-steering mirror (48) is used in embodiments, such as the one seenin FIG. 3A, where more than one science camera (e.g. visible lightcamera (53) and infrared camera (66)) is used in the system and thenonly if one of those two cameras is used to make high-speed image motionmeasurements.

With respect to the science cameras, the fast steering mirror (48) canbe used in one of two ways. In a first way, the fast steering mirror(48) can be set to a fixed position. If this is the case, the sciencecameras take fast images of the objects being viewed and correct forimage motion in the software after the images are taken. Alternatively,the fast steering mirror (48) can be commanded to stabilize an image oneither the visible light camera (53) or infrared camera (66) while theother camera (not being stabilized by the fast steering mirror (48)) isused to take long exposure images.

A visible dichroic (50) is used to interrupt the visible andnear-infrared light reflected by the third off-axis parabolic mirror(49) and reflects light with a wavelength under 950 nm, corresponding tovisible light, through a series of visible light filter wheels (52) andultimately to a visible light camera (53). The visible dichroic (50) isgenerally used when embodiment (such as the one in FIG. 3A) includesboth a visible light and infrared camera. In the embodiment of FIG. 3A,both the visible dichroic (50) and the visible light filter wheels (52)are in fixed mounts.

The visible filter wheels (52) each have a position for each of sixdifferent optical filters. The different optical filters allow thevisible light camera to access different parts of the transmittedvisible spectrum as each filter has a different upper and lowerwavelength cut off. The visible filter wheels (52) are optional and inother embodiments for the AO system (2), the AO system (2) can operatewithout the visible filter wheels (52). However, the filter wheels (52)do provide scientific benefit and therefore have been implemented asseen in FIG. 3A.

The visible light camera (53) captures the final images produced by thetelescope (1) and the AO system (2). The visible light camera (53) canalso be used to measure the image motion of a viewed object which canthen be stabilized with the fast steering mirror (48). If the imagemotion is stabilized in this way, long exposures can then be taken withthe infrared camera (66).

The visible dichroic (50) also transmits light with a wavelength over950 nm, corresponding to near-infrared light, to a gold-coated foldmirror (54). The fold mirror (54) uses a gold coating because gold isone of the best near-infrared reflecting materials. The near-infraredlight is then directed perpendicular to the light weight plate (39) andto the infrared camera (66).

The infrared camera (66) functions in the same manner as the visiblelight camera (53) but instead works at longer wavelengths (from about950 nm to about 2200 nm). The infrared camera (66) captures final imagesproduced by the telescope (1) and can also be used to measure the imagemotion of a viewed object which can then be stabilized with the faststeering mirror (48). Similarly to the situation with the visible lightcamera (53), if the viewed object is stabilized using the fast steeringmirror (48) with reference to the infrared camera (66), long exposurescan be taken with the visible light camera (53).

With respect to the UV light, corresponding to light under thewavelength of 390 nm reflected by the ultraviolet dichroic (43) to thecondenser lens (55), the UV light is folded by a flat laser mirror (56)before coming to a 10 km focus at an adjustable diameter field stop(57). The adjustable diameter is nominally 5 arcseconds. The flat lasermirror (56) is used to maintain the compactness of the overallinstrument as similar structures have been described above. Meanwhile,the 10 km focus is provided to be optically conjugate to the 10 kmdistance the laser beam is being propagated.

The adjustable diameter field stop (57) is an adjustable size iris in afixed optical mount, but is usually only adjusted during assembly of theinstrument. The adjustable diameter field stop (57) is used to restrictthe field of view of the wavefront sensor to a narrow angle (e.g., 5arcseconds). In this way, the grid of images on the wavefront sensor isconfined to specific pre-determined pixels.

In an alternative embodiment, one may provide an AO system without theadjustable diameter field stop (57). In such an embodiment, the AOsystem would have a different pixel readout from the wavefront detector(65), software to compensate for a shifting of the Shack-Hartmannpattern of images and different shuttering techniques. The benefit ofnot implementing the adjustable diameter field stop (57) would be thatit could potentially speed up laser acquisition process given that thewavefront sensor detector (65) would have a larger field of view.Additionally fewer steps would be needed in the spiral search algorithmwhich would also provide a speed up in laser acquisition.

Returning to FIG. 3A, the UV light then expands and is folded by asecond flat laser mirror (58) before being collimated by an off-axisparabolic mirror (59). The off-axis parabolic mirror (59) is used tooptically null out the coma induced by reflection off of the firstoff-axis parabolic mirror (41). If the coma is not removed, the comawill cause a large static error to be seen in the wavefront sensor.Alternatively, in other embodiments, one can use a Schmidt plate or aspherical correcting plate (of which are commercially available) withreference to a collimated beam to remove spherical aberrations which mayarise.

Such coma is induced because the laser focus was not at the radius ofcurvature of the first off-axis parabolic mirror (41). This can occurbecause light from the viewed object is at the center of the radius ofcurvature of the first off-axis parabolic mirror (41). Generally, onecan pick either or neither of the two images (corresponding to infinityfocus or 10 km focus) to be at the center of the radius of curvature butnot both. The present embodiment, shown in FIG. 3A, is arranged suchthat it can separately fix the coma in the wavefront sensor detector(65) easily.

The collimated UV light then passes through a first linear polarizer(60), a Pockels cell (61) and a second linear polarizer (62) orientedorthogonal to the first linear polarizer (60). The first linearpolarizer (60) is used to match the polarization of the returning laserbeam after it has been set by adjusting the half-wave plate (8) asdescribed above. The first linear polarizer (60) rejects any laser lightthat is not linearly polarized in the proper direction correspondingpossibly to reflection off of dust in the atmosphere.

The Pockels cell (61) is a dielectric crystal. If left alone, thepolarized light that passes through the first linear polarizer (60) willpass through the Pockels cell (61). Afterwards, the light will come toan orthogonally oriented second linear polarizer (62). The second linearpolarizer (62) will then stop the light from propagating further intothe wavefront sensor detector (65). On the other hand, if a potentialvoltage is applied across the Pockels cell (e.g. about 3500 V), thePockels cell will act as a half wave plate and rotate the polarizationof the linearly polarized returning laser beam that passes through it.Once the laser beam is rotated, it will transmit through theorthogonally oriented second linear polarizer (62) to the wavefrontsensor detector (65).

In other embodiments, the Pockels cell (61) as well as the first andsecond linear polarizers (60, 62) may be removed if some other way ofshuttering the returned laser beam is implemented to replicate thefunctionality of the above elements. For example, such embodiments mayinclude the use of electronically gated CCD detectors.

As previously stated above, Rayleigh scattered light from the laser beam(5) is used to measure (or probe) atmospheric distortion. With respectto the above mentioned Rayleigh scattered light from the beam of laserlight (5) used to measure (or probe) the atmospheric distortion, the AOsystem (2) is able to identify Rayleigh scattered light obtained fromthe laser beam (5) about ten kilometers away through the use of a signaldelay generator. The signal delay generator triggers a Pockels cellelectro-optic shutter to open after a calculated round-trip time for thelaser beam to travel 10 km and return back. In other embodiments, the AOsystem (2) can be reprogrammed to allow the laser beam from differentdistances (other than 10 km) to be measured.

The wavefront sensor detector (65) can potentially obtain other sourcesof light (i.e. not of the laser beam (5)) which the wavefront sensordetector (65) can mistake as coming from the laser beam (5). Suchundesired situations can arise, for example, when light is beingobtained from some very bright stars. To mitigate or minimize the effectof receiving contaminating light at the wavefront sensor detector (65),broadband metallic mirrors within the wavefront sensor detector can bereplaced with mirrors with a laser-line dielectric coating (like theflat laser mirror (56)).

With reference back to FIG. 3A, after the light passes through thesecond linear polarizer (62), a lenslet array (63) is placed at thereimaged pupil of the telescope (1) which spatially subdivides thereturning laser beam that entered the telescope (1) thereby creating aShack-Hartmann set of images of the laser. The Shack-Hartmann set ofimages allows the system to measure the local gradient of the light waveat the reimaged pupil. The lenslet array (63) is a refractive opticalelement which is flat on one side and with a grid of square-shapedconvex lenses on the other side. The lenslet array (63) is located at aposition optically conjugate to the entrance pupil of the telescope (1).When non-planar light from the laser beam (5) passes through the lensletarray (63), images of the laser are created at a focus of each of thelenses in the lenslet array (63).

The pattern of laser images is then optically relayed to a UV optimizedcharged-coupled device (CCD) camera by an optical relay (64). Lateralx-y positions of each laser image give a measure of a local gradient orslope of the non-planar light wave through each lens of the lensletarray (63). In other embodiments, the optical relay (64) may be removedif the wavefront sensor detector (65) were matched in size to thelenslet array (63).

The overall shape of the non-planar light wave is then calculated bymultiplying the measured slopes by a wavefront reconstructor matrix. Thereconstructor matrix converts the relative positions of theShack-Hartmann set of images to a set of correcting displacements forthe actuators in the deformable mirror (42).

The adaptive optical system (42) uses a reconstructor matrix that iscalculated by first making a model of the pupil geometry that issub-divided by the lenslet array (63). Individual ortho-normal basisfunctions are realized over the model of the pupil geometry and a 2-Dleast-squares solution to the best fit plane for each lens in thelenslet array (63) is calculated. An influence matrix is thus derivedthat converts unit amplitudes for each basis function with the slopeoffset for every lens. The reconstructor matrix is then created bytaking the pseudo-inverse of the influence matrix using Singular ValueDecomposition. The person skilled in the art will understand that theabove description represent one possible embodiment to allow use of thereconstructor matrices in the AO system (2), and that other embodimentsare also possible.

Once the shape of the non-planar wave is known in terms of coefficientsof the basis set, an inverse shape can be commanded on the high-orderwavefront corrector. This process then provides the correctionsnecessary to compensate for the distortion caused by the atmosphere. Theprocess of making a measurement, then applying a correction is repeatedmany times. As described above, such measurements may be performed at arate of 1.2 kHz in order to keep up with the dynamics of the atmosphere.

Attention is now drawn to a laser adaptor bracket, as seen in FIGS. 4and 5. The laser adaptor bracket allows attachment of the compact laserprojector system (4) to any telescope (1). One benefit for attaching thecompact laser projector system (4) to the telescope (1) is that itensures that the compact laser projector system (4) and the telescope(1) are always pointed in the same direction within the mechanicaltolerances of the telescope (1) and the laser adaptor bracket for thecompact laser projection system (4). This obviates the need to have aseparate pointing mechanism for the compact laser projection system (4).

FIG. 4 illustrates an example of an outlined laser adapter bracket thatcan be used to attach the compact laser projection system (4) to thetelescope (1). FIG. 5 shows the compact laser projection system (4)physically attached to the telescope (1) via the laser adapter bracket.The laser adaptor bracket is designed to adjust a crude pointing of thecompact laser projector system (4) in two directions.

With continued reference to FIGS. 4 and 5, the compact laser projectorsystem (4) attaches to the telescope (1) through the mounting points(18) to a top plate (19) of the laser adaptor bracket via correspondingpoints (20) of the laser adaptor bracket. A pivot pin (21) in the topplate (19) allows the compact laser projector system (4) to be manuallytilted in one direction by adjusting positions of push bolts (22).Furthermore, the compact laser projector system (4) can also be fixedinto location by tightening bolts (23) of the laser adaptor bracket.

To adjust the rough pointing of the laser adaptor bracket orthogonal tothe pointing provided by the pivot pin (21) of the laser adaptorbracket, preload bolts (24) are used to push against the structure ofthe telescope (1). By adjusting the amount of compression on the preloadbolts (24) of the laser adaptor bracket, an angle that the laser adaptorbracket makes with the structure of the telescope (1) can be adjusted.Additional bars (25) can be used in the laser adaptor bracket to match anormal direction of a telescope tube of the telescope (1) with respectto the preload bolts (24).

The laser adaptor bracket attaches to the telescope (1) via bolt holes(28) in the two platforms (26 and 27). Typically, observatory telescopesthat are greater than 1 m in size have some way of mounting instrumentsand electronics on them. However, mounting holes and platforms aredifferent from telescope to telescope, thereby requiring a differentlaser adaptor bracket for each different telescope.

Typically, the laser projection system has a very limited ability torepoint the laser beam (e.g. 160 by 228 arcseconds). The laser adaptorbracket shown in FIGS. 4 and 5 allows the change to be applied to thecompact laser projection system (4) by several degrees. This results ina very large manual pointing adjustment which can be done to facilitatethe laser beam (5) to be close to the alignment of the telescope (1).Afterwards, the robotic controls can provide fine adjustments to fix therest of the alignment. Furthermore, the laser adaptor bracket can alsocompensate for differential pointing as detailed in the software laseracquisition section.

Reference will now be made to an additional embodiment of the presentdisclosure, shown in FIG. 6. The embodiment, to be described below, isused if a user desires naked-eye viewing of the images being obtained bythe AO system (2). Such additional elements are not necessary for theoperation of the AO system (2).

Typically, an individual is unable to see images being obtained by theAO system (2) except through a display (such as a computer console)where the image being obtained is transmitted. According to the presentdisclosure, a further embodiment is provided, which enables anindividual to directly view an image being observed. In particular, theindividual would be able to view the visible light image within the AOsystem (2), through an eyepiece (93). Such light is the same visiblelight which is being reflected to the visible light camera (53).

As already noted before, visible light is normally reflected by thevisible dichroic (50) through visible filter wheels (52) and to thevisible light camera (53), as now shown in FIG. 6. However, it ispossible to allow an individual to view the image being transmitted viavisible light by adding additional components to the AO system (2).

In order to allow the individual to view the visible light transmittedwithin the AO system (2), first a beam splitter block (91) is used. Inparticular, the beam splitter block (91) comprises a visible beamsplitter (90) and is placed between the path of the visible light comingfrom the visible dichroic (50) and the visible light camera (53). Thebeam splitter block (91) is attached to the light weight plate (39)through magnetic bases (51) and (92), as shown in FIG. 6, to allow foreasy installation and removal of the beam splitter block (91).

Because of the presence of the beam splitter block (91), there is avariable amount of light that is sent to the eyepiece (93) and to thevisible light camera (53). The quality of the images is negligiblyimpacted but the amount of intensity can be reduced. Additionally,different types of visible beam splitters (90) may be used to change theamount of light split between the eyepiece (93) and the visible lightcamera (53). Alternatively to the beam splitter, a regular mirror can beused, to maximize the light sent to the eyepiece (93) at the expense ofbeing able to also use the visible light camera (53) simultaneously,since the regular mirror will prevent light from reaching the visiblelight camera (53).

The visible beam splitter (90), attached to the beam splitter block(91), reflects visible light out of the instrument, perpendicular to theplane of the light weight plate (39). The beam splitter block (91) alsohas a hole which allows the visible light not reflected off the visiblebeam splitter (90) to pass through to the visible filter wheels (52) andthe visible light camera (53).

To view the visible light which has been reflected by the visible beamsplitter (90), the eyepiece (93) is attached to an external structure(94) of the instrument enclosure of the AO system (2). Such externalstructure (94) can be realized through an eyepiece holder or a tube witha set-screw to securely hold the eyepiece (93) in place. Additionally,filters can be added to the eyepiece (93), if desired.

With the use of the eyepiece (93) without filters, a person is able tosee the images received by the visible light camera (53) in full color.The visible light camera, on the other hand, generally only recordsmonochrome images regardless of the visible filter used. These imagesviewed correspond to the images being received by the telescope (1).

Alternatively, in other embodiments, one can also use an adaptor to puta digital SLR camera in the same port as the eyepiece (93). This wouldallow a person to take full color adaptive optics corrected images.

Following the above description of the compact laser projection system(4) and the AO system (2), the present disclosure will now describe indetail the overall software and programming used to control the Robo-AOsystem.

Software/Methods

As introduced earlier in the present application, an aim of the presentdisclosure is to provide a system that is fully automatized and easilyreplicated. In other words, the Robo-AO system would be able toautomatically perform any calibration, correction and operationalprocedure necessary to obtain scientific measurements from a particulartelescope and that such a system would be useable with a wide variety ofdifferent telescopes. This is achieved by modularizing the varioussubsystems within the Robo-AO control system to allow greaterinterchangeability between the Robo-AO and the software/hardware thatthe Robo-AO manages. Although full automation is achieved in accordancewith the teachings of the present disclosure, the person skilled in theart will understand that manual intervention is still allowed, wheneverdesired, e.g. for maintenance purposes. In the following paragraphs, adetailed description will be provided as to implementations of aplurality of subsystems and their control system designs which are usedto control the respective subsystems of the Robo-AO control system.

According to several embodiments of the present disclosure, the controlsoftware used to run the Robo-AO is based on a client-serverarchitecture. By way of example, the software for the control can be C++based. Furthermore, the client-server architecture can be implementedover TCP/IP using a Linux® operating system. Although it would bepossible to incorporate the entire Robo-AO system (in other words therobotic control system and the various subsystems) into a singleprogram, an advantage of the current implementation is that it is morerobust. In particular, if any single subsystem of the Robo-AO systemcrashes, the rest of Robo-AO system would not be immediately terminated.

FIG. 7 shows an exemplary architectural layout for a control software ofthe Robo-AO system in accordance with the disclosure. The Robo-AOcontrol software includes a number of subsystem daemons andcommunication paths between the subsystems. The term ‘daemon’ as usedthroughout the present disclosure indicates a program, e.g. a controlprogram, running as a background process, rather than being undercontrol of a user. Alternatively, embodiments can be provided where theuser has direct control of the subsystems of the Robo-AO system, or evenover the operation of the Robo-AO system. In such embodiments, however,the system would not be fully automatized.

A robotic control system (100) (e.g. a daemon) manages the entireRobo-AO system. After being instructed to observe a particular object(or by selecting a particular object to be viewed based on a queue),scientific data will next be acquired from the object. Such scientificdata includes images of the object which are used to calculatemeasurements for the object. For example, in one embodiment, the objectsbeing viewed could be astronomical objects while the measurements beingtaken could be astrometric, photometric or spectroscopic. A moredetailed disclosure pertaining to how the robotic control subsystem(100) selects the object to be viewed will be described later below.

Also present in the control software are a number of sub-systems(101-108) that directly interface with different hardware or softwareinterfaces. Such subsystems, together with the robotic control system(100), accept commands and provide output subsystem statuses using acommunication system for control (114) and status monitoring (115).

According to an embodiment of the disclosure, the communication systemis a C++ based software that is developed to handle communications overTCP/IP connections. During operation, a server is started first. Next, aclient opens a connection and passes a message that the client isconnecting with the server. The server responds with a welcome messageand information about the particular server process is provided. If theconnection is successful, communication between the client and server isestablished. The client and server then send ASCII text strings back andforth to each other as appropriate to execute commands, share stateinformation and otherwise operate the Robo-AO.

A list of the Robo-AO subsystems (101-108) will now be provided. Detailsrelating to such system daemons will be provided later in thedisclosure, also with reference to the figures. Although the eightsubsystem daemons below are provided in detail, embodiments of theRobo-AO can have any number of subsystem daemons, more or less than thenumber being described throughout the present disclosure.

-   -   Telescope control subsystem daemon (101): used to send commands        to the telescope (1) for operations.    -   Laser beam guidance subsystem daemon (102): controls operation        of the laser beam guidance hardware.    -   ADC subsystem daemon (103): controls operation of the ADC (47).    -   AO subsystem daemon (104): controls operation of the AO system        (2).    -   Visible instrument camera (VIC) subsystem daemon (105): controls        operation of the visible light camera (53) and visible light        filter wheels (52) used to gather visible wavelength science        data.    -   Infrared camera (IRC) subsystem daemon (106): controls operation        of the infrared camera (66) and infrared filter wheels.    -   Telescope status control subsystem daemon (107): interfaces with        the telescope control system to monitor operational status of        the telescope (1).    -   Weather monitor control subsystem daemon (108): monitors a state        of observatory weather system and checks for safe environmental        operating parameters.

In this present embodiment, the above listed subsystem daemons, as wellas other potential subsystem daemons, are provided in such a way thatparticular processes are separate. However, in other embodiments, it ispossible to further separate operations of particular processes intomultiple different subsystems. Furthermore, it may be provided thatmultiple processes be combined into a single subsystem. As stated above,additional processes (or subsystems) could be added to the Robo-AOsystem as the above listing is not meant to limit the possiblesubsystems incorporated by the Robo-AO system. However, all the aboveembodiments maintain the goal that particular functions can bemodularized. Furthermore, such control structures would be implementedas a compromise between the operational capability of the system and itsmodularization.

Returning back to FIG. 7, the robotic control system (100), by using thecommunication system for control (114), is configured to automaticallydetect situations when a subsystem has disconnected or has crashed. If adisconnection is detected, the robotic control system (100) assumes thatthe connected subsystem has crashed and kills related processes tied tothe crashed subsystem. The robotic control system (100) then restartsthe subsystem through the use of a restart command. If the subsystemcannot restart after a predefined set of attempts, the robotic systemcontrol (100) logs the server failure and then shuts down.

The Robo-AO system control software also contains a system monitoringthread (109). The system monitoring thread (109) receives a status fromeach of the subsystem daemons (101-108) and sets flags for the operationof the robotic control system (100) based on the status. The systemmonitoring thread (109) is represented differently from the subsystemsin FIG. 7 because it is currently a separate thread inside the roboticcontrol system (100). However, embodiments are also possible in whichthe system monitoring thread (109) can be a separate subsystem.

FIG. 7 also shows a watchdog control system (112) which is used by therobotic system control (100) to monitor the status of the entire Robo-AOsystem and its operation. If an error is detected by the watchdogcontrol system (112) or if the robotic control system (100) crashes, thewatchdog control system (112) automatically takes over operationalcontrol of the robotic control system (100).

In the above situation when the watchdog control system (112) takes overoperational control of the robotic control system (100) when the roboticcontrol system (100) crashes, the watchdog control system (112) firstputs the robotic control system (100) into a safe state. Afterwards, thewatchdog control system (112) will attempt to restart normal operations.If a situation arises where the watchdog control system (112) is unableto restart after a predefined set of attempts, the watchdog controlsystem (112) may log the failure and then shut down the Robo-AO system.

The watchdog control system (112) contains all information from thesystem monitoring thread (109). In fact, the software used for thewatchdog status system in the watchdog control system (112) is thesoftware as in the robotic control system (100). If the robotic controlsystem (100) fails at something, the watchdog control system (112) sendssignals to the robotic control system (100) to pause. Furthermore, thewatchdog control system (112) will attempt to execute programmedoperations to fix the experienced failure. These programmed operationsinclude the same operations the robotic control system (100) runs aswell as more draconian measures to stop the robotic control system fromcontinued operation immediately (e.g., cutting the power). Once therobotic control system (100) has been placed in a safe state, thewatchdog control system (112) will take individual subsystems through aninitialization process. The entire Robo-AO system is stopped if any ofthe subsystems continue to fail.

All components of the Robo-AO system control software continually outputtelemetry and logging information to allow examination of the operationof the system via communication line (113). If desired, a multi-threadedmethod can be used to write log file statements. Such log filestatements are stored in hard drives (110). Throughout the presentdisclosure, the term ‘multi-threaded’, a technique where a program hasmore than one function executing in parallel, will be used to indicatemultiple threads existing within a same process during the execution ofa task. In the Robo-AO system, multi-threading allows an efficientfunctioning of the system.

Additionally, the outputted telemetry can also be written to memoryusing a multi-threaded method, similar to the logging system describedabove. With respect to the telemetry, such can have both high and lowspeed capabilities. The system telemetry outputs state values for eachof the subsystems as they operate. State values may include weatherparameters (such as temperature or humidity), camera parameters (such astemperature, cooler state and current instructions), motor parameters(such as position and motion state) and telescope status, among otherinformation. According to an embodiment of the disclosure, everythingthat can be recorded is done so into one or more hard drives (110).

The system telemetry is generally taken at 1 Hz although some systems(such as the AO system (2)) may desire telemetry at higher rates.Depending on a speed at which the system telemetry is taken at, theinformation is recorded in different locations. The low speed telemetrywrites its data to a file on the hard disk directly when gathered. Onthe other hand, the high speed telemetry writes its data into memory andgenerates a thread to write the telemetry to a file on the hard disk asnecessary. The high speed telemetry also makes new files automaticallywhen the file grows too large. In contrast, the low speed telemetry doesnot grow large enough to require additional space from a new file.

Additionally, image data can be saved, if desired, in a Flexible ImageTransport System (FITS) format via link (116). The image data can alsohave low and high speed capabilities, as similarly provided for theabove described telemetry data. Such capabilities are provided sincesome camera images are taken as long exposures while other imagesrequire a rapid readout from the camera system. The high speed FITS datais able to create FITS data cubes (i.e. three-dimensional arrays ofimage data) at a camera rate continuously. Additionally creation of newdata cubes can also be done on-the-fly, if desired.

All image data (e.g., astronomy image data) can be saved in a standardFITS format. Camera systems generally gather data from their respectivecameras and write the camera data, corresponding to pixels ofinformation, into FITS data files. An information header is added to theimage that contains information on the state of the Robo-AO system atthe time the observation was taken.

With respect to long exposures, the camera image can be written to adisk directly when the exposure is finished. However, when rapid readoutis used, the camera system gathers images one after another so fast thatwriting a single FITS file for each may be too slow. In such a case, aFITS data cube (which constitutes a stack of FITS images) is created andwritten to as each image is gathered. Once the FITS data cube is full,the FITS data cube is closed and another is created if more cameraimages are to be taken.

Discussion of the Robo-AO subsystem daemons (101-108) listed above willnow be provided in detail below. Reference is first made to FIG. 8,which shows a high level flow chart for the weather monitor controlsubsystem daemon (108) used to monitor the observatory weather systemand to check for safe environmental operating parameters. The weathermonitor control subsystem daemon (108) is the simplest of all thesubsystem daemons (101-108) previously described and will be used todescribe the general behavior of all other subsystems used within theRobo AO control system.

According to an embodiment of the present disclosure, all subsystems(including the weather monitor control subsystem daemon (108)illustrated in FIG. 8) of the Robo-AO system feature multi-threadedarchitecture. The use of multi-threaded architecture covers theimplementation where several threads are provided in a same process. Asshown, for example in FIG. 8, the multi-threaded architecture of theweather monitor control subsystem (108) has five main threads (command(116), control (117), status (118), error monitor (119) and watchdog(120)), which are used to monitor and control the operation of thesubsystem's respective hardware and software interfaces. Furthermore, inaccordance with an embodiment of the disclosure, the subsystems caninherit their respective properties from a base C++ class where somefunctions are defined in the base class to enhance performance andmodularity of the subsystem.

When a subsystem daemon is launched, four threads are initially created:the control (117), status (118), error monitor (119) and watchdog (120)threads. All threads start with their own initialization procedure (121)that is used to set variable states and prepare the respective threadfor operation. Such threads will also undergo a shut-down procedure(122) in order to terminate the thread in a proper manner, eithernaturally during operations or when the operation of the daemon ends.

The control thread (117) is the main management thread in the operationof each subsystem. The control thread (117) receives commands fromclients (e.g. other subsystems) connected to the particular subsystem(accept command (130)) and launches a fifth thread (the command thread(116)) (start command thread (131)) that executes the received commandsfrom external clients separately.

The command thread (116) undergoes its own initialization procedure(121) and then executes the received commands (execute command (133)),outputting a result (output result (134)) to a state variable that isread by the control thread (117). The control thread (117) thentransmits (transmit result (132)) the results of the command to theexternal client that provided the instructions to the command thread(116). Since the command thread (116) is independent from the otherthreads of the multi-threaded architecture, it is able to executeoperations while the control thread (117) continues to operate andcommunicate with attached external clients.

Although subsystem daemons (through the command thread (116)) usuallyaccept only one command at a time, commands can be queued for laterexecution if multiple commands are provided to the system. Such featurecan apply to all subsystem daemons described throughout the presentdisclosure.

With continued reference to FIG. 8, a status thread (118) is alsoprovided. In the specific case of the weather monitor control subsystemdaemon (108), the status thread (118) polls its respective hardware andthen writes a state to a weather state class container (get weather data(127)). The associated hardware for the weather monitor controlsubsystem (108) can be, for example, an observatory weather station andinternal thermal and humidity sensors.

The state stored in the weather state class container (127) is thenshared with the control thread (117). The control thread (117) transmitsthe state (129) to the clients at a rate of, e.g., 1 Hz. With referenceto the weather daemon (108), information is sent to the robotic systemdaemon (100) and the watchdog daemon (112) through the system monitorthread (109).

The fourth thread in a subsystem daemon is an error monitor thread(119), which is used to examine the operation of the subsystem daemonfor any anomalies (check for errors (125)). This operation includesexecuting functions that may help the subsystem daemon to providecorrect instrument operation (such as a hardware control interface,purely software functions, etc.). In the specific case of the weathermonitor control subsystem daemon (108), the error monitor thread (119)looks at parameters such as wind speed and temperature to see if anyconditions are outside the safe operating parameters of the observatory.The error monitor thread (119) can also monitor the connection to theobservatory weather station and flags an error in situations where thereare lost communications.

Additionally, the error monitor thread (119) can be used to change anoperating state of the subsystem for safety, or to start an automatederror control operation (correct errors (126)) to fix the error. In thecase of the weather monitor control subsystem daemon (108), this couldentail restarting the weather station communications.

The fifth thread of the multi-threaded architecture is the watchdogthread (120). According to an embodiment of the disclosure, the watchdogthread (120) is defined in the base class and is the same in allsubsystem daemons. The watchdog thread (120) monitors operation of theother threads (e.g. 116-119) to make sure that the other threadscontinue to operate properly (check for system failure (123)). Inparticular, the watchdog thread (120) tracks execution times of theother threads. This can be performed by requiring that the other threadswrite their respective current execution time into a variable that istracked by the watchdog thread (120). If one thread stops executing itscontrol loop, the watchdog thread (120) steps in.

The watchdog thread (120) can also examine variable settings or otherparameters to make sure they do not drift out of a set boundary. In afurther embodiment, the watchdog thread (120) is also able to monitormemory leaks or issues, processor usage of the other threads and otheroperating system parameters. The watchdog thread (120) is also able toadjust operation of the subsystem daemon accordingly.

The following are some exemplary cases where the watchdog daemon (120)undergoes different procedures to fix issues that arise in the subsystemdaemon. In one situation where one of the threads freeze, the watchdogthread (120) attempts to take over action of the frozen thread to fixthe situation. In another situation, the watchdog thread (120) can tryto stop the frozen thread and then restart the same thread. Wherevariable settings are drifting outside a set boundary, the watchdogthread (120) can provide a flag and reset the variable settings. Thewatchdog thread (120) can also change operational parameters such asupdating the rate of the status or control threads. Lastly, the watchdogthread (120) can even stop the entire subsystem daemon process, ifnecessary.

In a situation where a problem cannot be resolved (for example, if afrozen thread cannot be unlocked by the watchdog thread (120)), thewatchdog thread (120) can shut down the entire subsystem daemon (fixfailure or shutdown system (124)). Furthermore, all attached clients tothe particular subsystem daemon are alerted. Each client attached to thesubsystem daemon can then attempt to restart the shut-down subsystemdaemon.

When several clients attempt to restart a subsystem daemon, more thanone instance of the subsystem daemon can be created in the process.However, having multiple instances of the subsystem daemons to controlthe same piece of hardware is undesired. To avoid this, a subroutine ina client may use a random number generator to set a delay time beforeattempting to restart a subsystem. Once a subsystem daemon has started,another client that attempts to start the subsystem can identify fromthe operating system that the subsystem daemon is already running andmay abort the attempt to restart the subsystem. Additionally, even insituations where two or more instances of subsystem daemons are somehowstarted, the Robo-AO system can stop all the subsystem daemons andattempt to restart the subsystems again.

Reference is now made to FIG. 9, which shows an architecture for thetelescope status control subsystem daemon (107). The telescope statuscontrol subsystem daemon (107) is similar to the weather monitor controlsubsystem daemon (108) discussed above. The only difference between thetelescope status control subsystem daemon (107) and the weather monitorcontrol subsystem daemon (108) is that the telescope status controlsubsystem daemon (107) accesses a status of the telescope system,executes a different command set, and has different error controlprocedures.

In particular, the status of the telescope is accessed by sendingcommands over TCP/IP to a telescope control system (137). The status ofthe telescope (1) can also be determined by directly querying thehardware of the telescope (1).

With respect to the query action, the telescope (1) can have its owncontrol computer that can receive commands over a TCP/IP connection. Theconnection returns status and controls information over the sameconnection. The TCP/IP connection to the telescope has three separateports: one for weather, telescope status and telescope control subsystemdaemons. Alternatively, direct control of the telescope (1) is alsopossible but would require new interface software to be implemented.

As stated above, the telescope status control subsystem daemon (107) andthe weather monitor control subsystem daemon (108) have differentcommand sets and error control procedures between the two, which arebased on the respective subsystem daemon's functionalities. In fact,generally speaking, all the subsystem daemons (101-108) have their ownset of commands and error control procedures, which are based on theirfunctionalities. However, the programmatic operation of the subsystemdaemons (101-108) are all the same.

Reference will now be made to FIG. 10, which shows a softwarearchitecture of the telescope control subsystem daemon (101). Thetelescope control subsystem daemon (101) manages operation of thetelescope by sending sends commands to move the telescope (1) andoperates the hardware of the telescope (1). The telescope controlsubsystem daemon (101) sends commands over TCP/IP to the telescopecontrol system (137) that operates the robotic telescope.

Additionally, the telescope control subsystem daemon (101) can alsodirectly control the hardware of the robotic telescope. Through animplementation of another system that connects the telescope (1)directly to the Robo-AO control computer (and associated software), onecan use the telescope control subsystem daemon (101) to directly controlthe telescope hardware.

Because the Robo-AO system can layer the direct hardware interfaces inmodules that are then compiled into the subsystem daemons (101-108),generally these interfaces can be exchanged for new modules that talk toa different kind of hardware that do the same thing. For example, a newcamera can be used to replace an existing camera. In the presentapplication, it will be shown that the new camera only requires writinga new module pertaining to the direct connection for the camera to theRobo-AO. This allows the rest of the Robo-AO system that controls thecamera to remain the same.

With reference back to FIG. 10, the telescope control subsystem daemonstatus (136) indicates the status of the telescope control subsystemdaemon (101) and its operational state. On the other hand, the status ofthe telescope itself is monitored through the separate telescope statussubsystem daemon (107) described above.

FIG. 11 shows a software architecture for the ADC control subsystemdaemon (103). As discussed above, the ADC (47) corrects the effects ofdispersion of light that passes through the atmosphere. The ADC controlsubsystem daemon (103) monitors the status of the ADC hardware (138).When a command is sent into the ADC control subsystem daemon (103), itexecutes the command by sending signals to a motor control systemhardware (139). These commands move motors connected to prisms that areused to do the optical correction to compensate for the dispersion oflight caused by the atmosphere.

The position of an object (e.g. a star in the sky) is one factor whichinfluences the dispersion of light caused by the atmosphere which thetelescope (1) receives because the position of the object defines a pathfor which light travels through the atmosphere. Therefore, the ADC (47)constantly changes the position of optics to compensate for thedispersion as the telescope (1) tracks the object. Calculating thedispersion is a known math equation that depends on an angle of thetelescope above the horizon and is then used to provide angles for theprisms used to correct for the dispersion.

The above correction is performed in a motor position thread (140),which is launched when the ADC control subsystem daemon (103) starts. Inparticular, the motor position thread (140) takes input from thetelescope status control subsystem daemon (107) and uses the informationobtained to calculate a dispersion correction (141). The motor positionthread (140) is unique to the ADC control subsystem daemon (103).

After the dispersion correction is obtained, the prisms are thencommanded to move accordingly (142) to compensate for the dispersioncaused by the atmosphere. The motor position thread (140) runs at a rateof, e.g., 1 Hz and continually updates the position of the prisms basedon the position of the telescope (1).

Parameters for and limits on the update position of the prisms areusually controlled through a configuration file. The configuration fileis created by a user and includes information that affects the operationof the ADC. This information can include limits to operation fromzenith, connection information for the motor controller and informationabout the ADC design that sets the axes of rotation. The configurationfile is located in a standard configuration directory, along withconfiguration files for all Robo-AO systems. For example, standarddirectories for telemetry, data and configuration files can be provided.The location of such files is included in the lowest level C++ classcommon to all Robo-AO software.

Next, FIGS. 12-1 and 12-2 show the software architecture for a visibleinstrument camera (VIC) control subsystem daemon (105). As with theother subsystem daemons, such as the ones discussed above, the VICcontrol subsystem daemon (105) monitors the status of the hardware itcontrols (e.g. the VIC). In the embodiment shown in FIGS. 12-1 and 12-2,the VIC control subsystem daemon (105) controls a VIC CCD (144) and anyattached filter wheels (143). The communication protocol can depend on acamera-hardware connection. By way of example, the Robo-AO VIC can useCameralink®. Alternatively, USB®, Firewire®, TCP/IP as well as otherhardware protocols can also be used instead.

According to an embodiment of the disclosure, the VIC camera system canhave three modes that are used to take images: regular camera images,rapid readout image sets, and tip tilt control images. The tip tiltcontrol images are used to correct a positioning of the telescope (1) toproperly acquire an object (e.g. target in the sky).

In the situation where the VIC camera system wants to take regularcamera images, such command is sent first to the VIC control subsystemdaemon (105). The command is accepted by the control thread (130) withinthe VIC control subsystem daemon (105). Then the control thread (117)starts a command thread (131). The command thread (116) executes thecommand and takes a single exposure of the VIC. The filter wheelposition is similarly controlled by the VIC control subsystem daemon(105).

On the other hand, when the VIC camera system wants to take a rapidreadout set of images, a separate rapid image readout thread (150) isgenerated. After initializing the rapid image readout thread (121), therapid readout thread (150) waits for a signal from the VIC controlsubsystem daemon (105) to start operations.

Once the VIC CCD (144) is configured properly for operation, the signalto start operations is sent and the rapid readout thread (150) starts togather images (151). Commands are sent to the VIC CCD (144) using thecamera interface software to set up its operational parameters accordingto an observing mode. That includes setting cooler temperatures,configuring the camera readout amplifiers and setting gain values. Afilter wheel position is set if necessary (147) by the rapid readoutthread (150). Filter wheel setup is typically done before starting therapid readout thread (150) by a separate command that goes through thecontrol thread.

Afterwards, the camera system starts a loop that takes an image off theVIC CCD (152) and writes the images to a disk (153) or a local systemhard drive. This ensures that the images are not lost if an error arisesduring operation. The rapid readout thread (150) gathers images byrequesting an image from the camera and then waits for the camera toreturn an image or an error. The operation of the camera is the same asfor the command thread (116) when setting up and observing a singleimage, except that the setup is done once and the imaging is repeated ina loop (with respect to the rapid readout thread (150)) instead ofwaiting for an external command to execute each observation.

The loop continues to operate until a stop signal is sent (stop (154)).After the stop signal is received, the rapid readout thread (150)returns to waiting for the next signal to start.

With reference to the third mode, taking tip tilt control images, a tiptilt image thread is launched as a separate thread (146) when a tip tiltcommand is sent to the AO system (2). As discussed above, the tip tiltimages are used to correct the positioning of the telescope (1) in orderto properly acquire an object.

After initializing the tip tilt image thread (146), the filter wheelposition is set (147), if required. Afterwards, the tip tilt imagethread starts a sequence of taking an image (148) and measuring acentroid position of the target star in the image (149). Images areacquired constantly during operation of the tip tilt image thread (146)until the tip tilt system is stopped. Measurements of the centroidposition of the target start in the images acquired are made for everyacquired image.

The centroid position is saved in a state variable that the controlthread (117) picks up when the centroid position value has changed. Inparticular, the centroid position values for the current measurement areheld in memory until the correction is completed. The centroid positionvalues are then replaced by the next centroid measurement. Centroidposition values are also included in telemetry.

The control thread transmits (155) the centroid position value to the AOsystem (2) which then uses the centroid position value to correct theposition of the telescope so that it can properly observe the object(e.g. a star in the sky). The control thread (117) also monitors theupdate time of the tip tilt thread (146). When the time changes, thecontrol thread (117) outputs new centroid values over client-serverTCP/IP connections to all clients. The AO system (2) is a client of theVIC control subsystem daemon (105), so the tip tilt centroids areautomatically sent to the AO system (2), which calculates new tip tiltmotor position and moves the tip tilt motor accordingly.

All VIC CCD data obtained above is recorded into FITS data files. Theregular images are recorded in a single two-dimensional image. Rapidreadout and tip tilt images are recorded in data cubes by recording, forexample, the data on demand, and creating new data cubes once thecurrent cube reaches a set size (e.g. 1 GB).

Image headers are provided for the images using a status of all theother Robo-AO subsystems at the time of observation. The purpose of suchdetailed image headers is to create a complete picture of the state ofthe Robo-AO system at the time the image was taken.

Next, FIGS. 13-1 and 13-2 show the software architecture of the IRCsubsystem daemon (106). The IRC subsystem daemon (106) is constructed ina similar way to the VIC subsystem daemon (105) discussed above.Therefore, all functions of the IRC subsystem daemon (106) operate in acomparable way to the functions of the VIC subsystem daemon (105), withthe exception that the IRC subsystem daemon (106) connects to aninfrared (IR) detector (157).

The IRC subsystem daemon (106) and the VIC subsystem daemon (105) areinterchangeable, as they both perform the same functions. As discussedabove for the VIC subsystem daemon (105), the IRC subsystem daemon (106)also gathers image data in regular and rapid readout modes as well asacquires and calculates tip tilt image centroids for the AO system (2)in a similar manner.

FIGS. 14-1 and 14-2 shows a software architecture of the AO subsystemdaemon (104). In the embodiment of the figure, the AO subsystem daemon(104) directly controls several pieces of hardware: the wavefront sensordetector (65), the deformable mirror (42) and the fast steering mirror(48) of the AO system, and the moveable beam steering mirror (9) of thecompact laser projection system (4).

As discussed above, the point of modularizing the Robo-AO system is thatthe AO subsystem daemon will not change, but differenthardware/interface software can be plugged into the AO subsystem daemonto control different pieces of hardware. For example, a differentwavefront sensor detector can be used in place of a current wavefrontsensor detector without significant (if not any) changes to the AOsubsystem daemon.

The hardware that can be controlled by the Robo-AO software includesmotor motion controllers, camera systems, electronic systems and datacollection systems. The Robo-AO software accesses these various hardwarethrough the hardware link to the computer (e.g. USB, Firewire, TCP/IP)and through the Linux operating system drivers that connect programs inthe operating system to the hardware.

The lower level hardware each have a software interface created for itwithin the Robo-AO software. The software interfaces (modules) can beplugged into the Robo-AO software as necessary to connect the commandinterface of the subsystem daemons to the hardware that the subsystemdaemon controls.

Returning to FIGS. 14-1 and 14-2, the status of the AO system ismonitored in the status thread (118) of the AO subsystem daemon (104).The AO performance is monitored at a rate of 1 Hz. In a similar manneras described for other subsystem daemons above, if an error is observed,the watchdog thread (120) steps in and attempts to correct the error aswell as sends a message to clients that an error has been detected.

The AO subsystem daemon (104) has the five standard threads describedabove (command, control, status, error monitor and watchdog) but alsohas two extra threads, which are launched when the AO subsystem daemon(104) starts: the tip tilt image thread (171) and the wavefront sensor(WFS) thread (178).

The tip tilt image thread (171) is used to stabilize X-Y positioning ofan object (e.g. target star) on the science camera (either VIC or IRC,depending on the operating mode). The stabilization corrects foratmospheric distortions and telescope and instrument motions that movethe object around on the camera.

After the tip tilt image thread (171) is initialized (121), the tip tiltimage thread (171) waits for a start signal to be sent to begin thecorrection process (172). The tip tilt image thread (171) waits for acentroid measurement (173) from the current camera. Although FIG. 14shows that the camera used is VIC (105), it should be noted that IRC(106) can be used instead.

Once the centroid measurement is received from either the VIC or IRC, acorrected position is calculated (174) by comparing the new centroidmeasurement and previous centroid measurements and applying a gainvalue. The correction is then sent from the tip tilt image thread (171)to a AO tip tilt motor interface (177). The AO tip tilt motor is given avalue that tells the motor a position to move to. The exact method ofcommunication depends on the interface to the AO tip tilt motor.

The loop of acquiring centroid measurements, calculating a correctedposition and providing the correction to the AO tip tilt motor interfaceis continued until the tip tilt image thread (171) is signaled to stopthe correction. At this point, the tip tilt image thread (171)terminates the loop (176) and waits for the start signal.

Turning now to the description of the WFS thread (178). The WFS thread(178) is the heart of the AO system (2) because it does the correctionfor the atmospheric turbulence/distortion of the light from the object(e.g. star in the sky) for the AO system.

After initialization, the WFS thread (178) waits until a start signal issent to begin the correction process (179). The signal to start thecorrection process (179) used with the WFS thread (178) is notnecessarily the same signal sent to the tip tilt image thread (171)because the two threads (the WFS thread (178) and the tip tilt imagethread (171)) operate independently.

Once the WFS thread (178) receives the signal to start, the WFS thread(178) initiates a correction loop. The correction loop for the WFSthread (178) runs at a rate of at least 1.2 kHz. Clients attached to theAO subsystem daemon (104) sends start commands for the WFS thread (178)thereby changing a state of a variable signifying whether the WFScontrol loop is paused or in an operational loop.

The AO system (2) commands the WFS CCD (185) to take an image to measurethe wavefront (180) of the laser beam (5). The WFS image is a set ofsubapertures created by a lenslet array (63) in the AO system (2). Eachsubaperture is generally a square of four pixels. The centroid of eachof these pixels is measured where generally the subaperatures do not allhave the same centroid. The difference in centroids is due to theturbulence of the atmosphere plus the optical distortions of thetelescope (1) and the AO system (2).

The WFS thread (178) then uses the frame to measure the distortion ofthe image and reconstructs the image to remove the effects ofatmospheric turbulence (181). To reconstruct the image, the measuredcentroids are converted to slopes adjusted for static distortions in theAO system (2) and then converted to deformable mirror movement positionsby using a previously constructed matrix that converts slopes todeformable mirror movements. The static distortions in the AO system (2)were previously measured as part of the AO system calibration.

With respect to deformable mirror movements, the commands are sent tothe deformable mirror (42) through a hardware interface. The deformablemirror does not actively transmit its position to the AO subsystemdaemon (104). However, determination of how successful the deformablemirror movements have been implemented is determined by measuring thenext WFS CCD image. Depending on the results, another correction can beapplied. Alternatively, if the deformable mirror is not operatingproperly (e.g. deformable mirror should be moving but it is readilyapparent that it does not), the status and error control threads willnote the problem, step in and attempt to fix the situation.

The above reference describes how a particular deformable mirror worksin the present embodiment. As with all hardware interfacing, otherdeformable mirror may work differently. However, the overall Robo-AOsystem will still be operational in a similar manner regardless of whichdeformable mirror is used.

The X-Y position of the laser beam (5) is also measured in the WFS CCDimage. The corrections for the laser beam (5) are obtained from themeasurements so that the laser beam remains centered in the WFS CCDfield of view. The commands to implement the corrections for the laserare sent to the tip tilt motor interface (187).

With reference to the corrections for the laser beam (5), tip and tiltmeasurements in the centroids of the WFS CCD images are due to movementsof the laser across the sky. Measuring the tip and tilt values allowscorrections of the laser position. This is similar to how the AO systemcorrections are measured and calculated. Instead of the tip and tiltmeasurements being sent to the deformable mirror as described above, themeasurements are provided to a laser motor instead. Each measurement ofthe tip and tilt provides new correction for the laser through the tiptilt motor position. This constant correction allows the laser positionto be continually updated.

In an embodiment of the present disclosure, the tip tilt motor commands(for the laser and the AO system) are sent through the deformable mirrorcommand interface corresponding to a particular feature of thedeformable mirror electronics system, which facilitates the corrections.However, as stated above, this particular hardware interface may beunique to Robo-AO based on particular hardware present. Otherembodiments can utilize different lasers and/or deformable mirrorhardware interfaces but essentially the same software of the Robo-AO canbe used. Again the significance is to allow replication of the Robo-AOcontrol system and increased modularity of the different subsystemscontrolled by the Robo-AO.

With reference back to FIGS. 14-1 and 14-2, the above loop for laserposition correction is continued until the AO subsystem daemon (104) issignaled to stop the correction. At this point, the WFS thread (178)terminates the loop (184) and waits for a future start signal to resumecorrections.

Now discussion will turn to FIGS. 15-1 and 15-2 which show the softwarearchitecture of the laser beam guidance subsystem daemon (102). Thelaser beam guidance subsystem daemon (102) controls all operations ofthe compact laser projection system (4). The status thread communicateswith the compact laser projection system (4) to read the laser status(188). The laser beam guidance subsystem daemon (102) also directlyoperates the laser hardware (189) when a command thread (116) isexecuted.

The laser safety shutter (7) is also controllable through the commandthread (116) of the laser beam guidance subsystem daemon (102). Thelaser safety shutter (7) is used to stop the laser beam from propagatingout of the compact laser projection system (4) as an additional safetymeasure as stated above.

Aside from the five threads that all subsystem daemons contain, asdescribed above, the laser beam guidance subsystem daemon (102) also hasa laser safety thread (191) that is launched when the laser beamguidance subsystem daemon (102) starts. The laser safety thread (191)monitors operation of the laser to insure that the laser only operateswhen it is safe to do so.

After initializing the laser safety thread (191), the laser safetythread (191) goes into a continuous loop that has several safety checksthat are done. First, the laser safety thread (191) checks the status ofthe telescope (192) and if the telescope is communicating properly. Thelatter is obtained by reading the telescope status control subsystemdaemon (107). If communications with the telescope status controlsubsystem daemon (107) fail, or if the telescope has a safety issue, thelaser safety thread (191) throws a flag to indicate the occurrence ofthe failure.

Next, the laser safety thread (191) checks that the laser closurewindows are open for firing. Typically, the Robo-AO system clearsoperations with USSTRATCOM®, which sends open windows to laser operatorsto avoid lasing of satellites. In situations where there exists a laserclosure window, which is generated by USSTRATCOM®, the closure windowsare handled automatically by the Robo-AO system.

The last check made by the laser safety thread (191) is regarding safeoperation of the laser hardware (194). If there are any issues with thelaser firing, the laser system operations are stopped (195), andoperations are not allowed to restart until it is again safe to do so.

Discussion has been provided relating to the subsystem daemons (101-108)as shown in FIG. 7. Additionally, the Robo-AO system can also beprovided with two additional subsystem daemons: a queue scheduler and apower system.

The current observing system is embedded inside the robotic controlsystem (100). The robotic control system (100) takes a predeterminedlist of objects (e.g. astronomical objects) and observes them in order.A simple facility is in place to skip observations for unavailabletargets (concerning laser closure windows) or objects that are notobserved successfully (due to system errors). Furthermore, theseobservations can be repeated if necessary.

This is contrasted with the queue scheduler subsystem daemon, which hasa library of available objects to observe. The observation informationfor the available objects is stored, for example, in an XML format file.The queue scheduler daemon is able to check a number of differentfunctions or parameters such as current conditions (such as telescopeposition, weather, atmospheric seeing), laser closure window times,target access and observation parameters. The queue scheduler daemonthen ranks the observation targets based on functions or parameters. Theobservation target that is ranked first after these checks performed bythe queue scheduler daemon is passed to the robotic observing system(100) to be observed. After the observation of the target is complete,the object is taken out of the list of available observations. The queuescheduler daemon allows the robotic observing system (100) to selectfrom thousands of targets at a time but also increase observingefficiency and scientific output over the current method.

The other additional daemon mentioned above which could also beimplemented in the layout of FIG. 7 is the power system subsystemdaemon. All the hardware for the robotic control system (100) is pluggedinto a network power switch (NPS), which can be controlled by computercommands. In the current embodiment, power switching is handled by eachsubsystem daemon separately as necessary. This can cause issues if twosubsystem daemons attempt to command the NPS at the same time.

Alternatively, a central power system can be implemented to solve theabove issue. In particular, the power system subsystem daemon canmonitor the state of the power system and handle switching in anintelligent manner. Clients (which can include all Robo-AO subsystems)will send commands to turn the power on or off and to check the state ofthe power switch. The power system subsystem daemon will be able tomonitor the state of the power switch, and if there is a failure, signalthe clients that there is an error. This signal can be used by therobotic control system (100) to stop operations. Furthermore, queuedpower switching, or sending a signal to switch multiple systems at onetime are possible implementations to increase efficiency relating to theoperation of the system. Additionally, the queued power switching andsimultaneous switching of multiple systems can also enhance safetyespecially in emergency conditions where all power can be instantlyswitched off at once.

Reference is now made to FIGS. 16-1 and 61-2, which shows the basicarchitecture of the subsystem daemon of the robotic control system (100)as seen, for example, in FIG. 7. As the central control system for theRobo-AO system, the robotic control system (100) can access informationfrom all the other subsystem daemons (e.g. 101-108). Furthermore, therobotic control system (100) can also send commands to the othersubsystem daemons (101-108) for the other subsystem daemons (101-108) toexecute scientific observations.

The robotic control system (100) has a multi-threaded structure similarto the other subsystem daemons. After initialization of the threads, thewatchdog thread (120) monitors operations of the robotic control system(100). Similarly, if the robotic control system (100) experiences afailure, the watchdog thread (120) either fixes the error or shuts thedaemon down.

Typically, in accordance with the present disclosure, if a subsystem hasa failure (such as a camera cooling shutting off or the laser notstarting properly), the error monitor thread of the subsystem that hasan error passes an error message to clients connected to it.

The error monitoring thread (119) receives errors from the subsystemsthat occur during operations (as opposed to errors that occur duringexecution of a command). The error monitoring thread (119) of therobotic control system (100) also receives the error message providedabove. In most cases, the error monitoring thread (119) makes adetermination if the error identified requires the robotic controlsystem (100) to stop operations.

It should be noted here (as similarly stated above) that aside from therobotic control system (100), all connected clients receive errormessages from any connected subsystem daemon so that such clients cantake appropriate action. Each of the subsystems of the Robo-AO system isindividually responsible for its operations, so that errors affectingthe various subsystems are handled locally. Additionally, the roboticcontrol system (100) sends commands to back up the operations done atthe local level or to monitor the subsystems to ensure that thesubsystems perform the right action in response to the error. The endresult is that such a system allows for better flexibility because eachclient subsystem does not necessarily take the same action when the sameerror is encountered.

For example, with respect to an laser beam guidance subsystem, asituation may arise when dealing with a closure. In a situation wherethe telescope communications show an error that is communicated to boththe robotic control system (100) and the laser beam guidance subsystemdaemon (102), the latter can immediately stop laser operations forsafety reasons to handle the problem at a local level. Alternatively, ifthe error is provided just to the robotic system (100), which would thencommand the laser beam guidance subsystem daemon (102) to stop thelaser, it is possible that the error signal and/or the command providedto the laser beam guidance subsystem daemon (102) could be delayed ormissed thereby causing the laser not to shut down properly. However,once the error has been cleared, the robotic control system (100) willcontinue normal operations.

As seen in FIG. 16, a system monitor thread (109) has been created as athread inside the robotic control system (100). However, the systemmonitor thread (109) could also be a separate subsystem daemon as well.

After initialization, the system monitor thread (109) reads the state ofeach of the subsystem daemons (101-108) through the client-serverconnections. All the subsystem daemons (101-108) send their statecontinuously to their respective clients.

As each subsystem daemon state is checked, flags are set to indicate thestatus. For example, a weather state flag is set when the weathermonitor control subsystem daemon (108) is checked. If any of the weatherparameters are outside of a predefined safe operational limit, the flagis set to indicate to the robotic control system (100) that the roboticcontrol system (100) should stop operations and wait until the weatheris safe for operations. In fact, each check of a subsystem daemon setsflags that indicate to the robotic control system (100) if operationsshould pause, continue, or completely stop.

The above operation of checking status/states and setting flagscontinues the entire time the robotic control system (100) is inoperation. Any failure of the system monitor thread (109) can be caughtby the watchdog thread (120). Without proper operation of the systemmonitor thread (109), the entire robotic control system (100) may notoperate safely.

Returning to FIG. 16, discussion now turns to the observation thread(209). The observation thread (209) controls the scientific operation ofthe robotic control system (100). The observation thread (209) undergoesinitialization (121). The initialization (121) includes additional stepssuch as initializing all subsystem daemons, preparing the telescope foroperation, waiting for cooling systems to cool instrumentation, takingcalibration frames and then waiting for the system monitor thread (109)to clear the observing thread (209) for operations.

Once operation of the observation thread (209) starts, the observationthread (209) goes through a sequence to gather scientific observations:

-   -   Select the next object (e.g. an astronomical object) from the        observing queue (211).    -   Configure the Robo-AO system (i.e. all subsystem daemons) for        observations (212).    -   Point the telescope (213) towards the targeted object (213).    -   Start the laser beam guidance system (214).    -   Start the AO system (215).    -   Take appropriate scientific observations (216).    -   Stop the AO system (217).    -   Stop the laser beam guidance system (218).

The above sequence continues until the robotic system (100) is pauseddue to weather or other instrument issues. The system then continueswhen it is safe to operate again. At the end of the night, theobservation thread (209) shuts down all subsystem daemons and terminatesall operations (219) of the robotic control system (100).

As discussed above, the watchdog control system (112) (as seen in FIG.7) monitors operation of the entire system with its own embedded systemmonitor. If the robotic control system (100) has a failure, or any othersubsystem daemon has an error to which the robotic control system (100)does not react, the watchdog control system (112) can take over andhandle the error.

For example, if the observation thread (209) of the robotic controlsystem (100) experiences an error, the watchdog control system (112)will attempt to restart the observation thread (209). If the watchdogcontrol system (112) is unable to restart the robotic control system(100) successfully, the robotic control system (100) is shut down. Asubsequent email message is provided requesting human intervention.

Reference is now made to FIGS. 17-1 and 17-2, which show a detailed flowchart of the observation thread (209) of the robotic control system(100). The flow chart shows execution of the observing loop during eachiteration for obtaining scientific observations when made for therobotic control system (100).

In the first step of the observing loop, the observation thread (209)determines the next target to observe (220). The target for observationis defined as a set of objects (e.g. astronomical objects) that togethercreates a scientific observation as part of an observation program.Targets can also be composed of multiple astronomical objects. Once atarget is selected, the next object to be observed is selected (221).Then the next observation for that object is selected (222).

The observation thread (209) can execute filter changes, ditherobservations, or other operations for the astronomical objects thatrequire multiple exposures as part of an observation. The observationsetups to be executed by the observation thread (209) are configured bythe scientists responsible for the observations and provide the desiredparameter.

Once the target is selected, the robotic control system (100) starts theobserving sequence. In parallel operations, commands are sent to movethe telescope (223), to configure the AO system, to configure thescience camera (227) and move the filter wheel if necessary (228). Whenconfiguring the AO system, the robotic control system (100) controlsboth the tip tilt (225) and WFS (226) systems.

The robotic control system (100) is capable of checking if the aboveoperations running in parallel with the observing sequence are completedsuccessfully (224, 229). Once the systems and hardware are configured,the observation thread (209) moves to the next step. However, if acommand failure occurs, the error monitor thread (119) of the roboticcontrol system (100) takes over and attempts to determine the error andfix it. Command errors are communicated back to the robotic controlsystem (100) from the subsystem daemons. In the event that the commandfailure results in an error, which is unrecoverable, the robotic controlsystem (100) will shut down and send an email for human intervention. Assimilarly discussed above, this error control paradigm is used for allRobo-AO functions.

The next step of the observation thread (220) is to propagate the laser(230) and check that the laser is operating properly (231). If it isfound that the laser is operating properly, the laser beam guidancesystem to acquire the laser is started (232). The system then waitsuntil the laser is acquired on the WFS CCD (223).

Once the laser is acquired on the WFS CCD (223), the AO system isstarted and the loop relating to the laser is closed. The loop relatingto the laser aims to keep the laser in position and starts the activewavefront correction with the deformable mirror (234). If there are noerrors (235), the robotic control system (100) starts setting up forscience observation of the targeted object. The tip tilt system sets thereference object to a particular spot on the science CCD (236). Once inplace, the AO system is calibrated (238).

In parallel to the calibration of the AO system, a reference seeingmeasurement is made (240). This measurement is used to measure theperformance of the system. If there are no errors (237, 239), the tiptilt loop is started (241). Afterwards, once the tip tilt loop beginsoperation, science observation is executed.

After a science observation is finished, the observation thread (209)checks to see if the observation was successful. If an error happensduring the science observation (244), the observation is attemptedagain.

After completion of the science observation, the observation thread(209) steps through any other exposures associated with the observation.Some observations are repeated multiple times so a check for a repeat ismade (246). If a repeat is required, the science observation is executedagain for the same target.

Furthermore if the same object is observed in multiple filters (247), afilter change is made (228, 248) and the science observation completedfor the object. If a dither observation is required (249), in otherwords situations where the telescope position is shifted, then theentire observing sequence is repeated with the new telescope alignment.

If after all of the above steps, there are still exposures to executefor the science observation (250), the required reconfiguration of thescience camera (227) and the subsequent scientific observation areexecuted.

Once the science observations for the object are all complete, theobservation thread (209) is ready to move to a new astronomical objectfor the next set of observations. The tip tilt system is stopped (251,252), followed by the stopping of the WFS system (253, 254) as well. Thelaser beam guidance system is stopped next (255, 256). Afterwards, acheck on queue targets is made (257). If the queue target still hasobjects available for observation, the object is selected. Otherwise,the current target is marked completed and a new queue target isselected (220). After the selection of a new object, the sequence startsagain.

Earlier, the application described the operations of the laser beamguidance system. FIG. 18 shows a flow chart for the operation of thelaser beam guidance subsystem. The laser beam guidance subsystem usesthe WFS CCD and laser steering mirror in concert to find the spot thelaser creates in the sky and center the spot on the WFS CCD.

The laser beam guidance subsystem is built into the AO system (2), butuses the compact laser projection system (4) to propagate the laser beaminto the atmosphere. Generally the AO system (2) is calibrated beforeoperating.

The robotic control system (100) first checks for a safe operating stateof the AO system (259) through the system monitor thread (109). Next,the compact laser projection system (4) propagates a laser beam (5) witha command from the laser beam guidance subsystem daemon (102). If thelaser propagation is successful, the AO system is calibrated (261).

With respect to the WFS CCD, when the background image is taken (261),Pockels cell (61) stops allowing light from the laser beam through(except for a slight amount). This slight amount allows measurement ofthe background in UV light. That background measurement is removed fromevery image taken with the WFS CCD during AO operations (both during theautomated laser search and AO correction). The laser beam is thenmeasured by the WFS CCD images to capture, align and center the laserbeam. Leftover light is due to the laser light being scattered. Verylittle UV light from astronomical objects can reach the ground.

Calibration using the laser beam is accomplished by taking a backgroundimage, which increases the performance of the WFS CCD. Once these stepsare accomplished, the automated laser acquisition function is run (262)by sending a command to the AO subsystem daemon (104).

The automated laser acquisition function then starts out by initializingvariable and array values to initial states (263). The automated laseracquisition function also resets the moveable beam steering mirror (9)to its center position, and initializes the operation of the WFS CCD.Once the initialization is complete, an initial image is taken with theWFS CCD (265).

A WFS CCD image is divided into several sub-apertures. In eachsub-aperture of the WFS CCD images, a total brightness and centroid aremeasured (266). For laser centering automation, the measuring ofbrightness in each sub-aperture allows to mark a sub-aperture as“acquired” when the sub-aperture brightness is greater than a presetthreshold.

When the initial WFS CCD image is taken, the number of acquiredsub-apertures are counted. If the number of acquires sub-aperturesexceed a preset percentage of the total number of sub-apertures, thenthe search is stopped (268). If the number of acquired sub-apertures isbelow the acquisition threshold, then the moveable beam steering mirror(9) is moved one step in a set direction (271) and another WFS CCD imageis taken and analyzed (266, 267).

The moveable beam steering mirror (9) is moved a preset anglecorresponding to a physical motion of the motor associated with themoveable beam steering mirror (9). The physical motion for moving themoveable beam steering mirror (9) is done in a spiraling pattern fromthe center of the motor range to its limit of travel.

The above procedure is repeated for each position of the laser steeringmirror (270) until the number of acquired apertures exceeds the setpercentage. If the search fails to acquire the laser beam (269), anerror is sent to the robotic observing system (100). Failure states caninclude (but are not limited to): poor WFS CCD backgrounding, lasershutoff, clouds or atmospheric phenomena, or an extremely brightbackground source.

The adaptive optics handles failures by re-measuring the background andattempting the centering procedure again. However, if the AO systemfails enough times the robotic control system (100) skips to anotherobserving target.

When the acquisition is successful (268), the spiral search is stoppedat that position. Continued searching after acquisition is inefficientand unnecessary. However, a second, finer search can be run at thispoint (273), using the same procedure as the first spiral search butwith a higher threshold for the percentage of acquired sub-apertures anda smaller step size.

Once the search for the laser beam is finished, a log message of theresults of the search is produced that details what happened during theautomated search process (272). A success or failure message is sent tothe robotic control system (100). If the search was successful, therobotic control system (100) takes another AO system background image(261) and then starts operation (274). This additional step is used toincrease the performance of the AO system operations.

The laser beam guidance subsystem position is then measured by firstcentroiding the sub-apertures. Afterwards, the laser beam is steereduntil it is centered in the sub-apertures. This sub-aperture centeringcontinues throughout the time the adaptive optics system is operating,automatically keeping the laser aligned on the sky with respect to thetarget.

Successful operation of the laser beam may require several steps.Although commands to the laser beam guidance subsystem daemon are sentthrough a connected client connection and can be done manually, when therobotic control system (100) is operational, the following operationsare done automatically.

With respect to the laser beam guidance subsystem, after installation ofthe laser, laser chiller and all hardware connections, the laser beamguidance subsystem is powered on with a command sent to the laser beamguidance subsystem daemon that powers the laser on using the NPS system.For example, an embodiment might use a laser which requires 90 secondsto power up and start communications with the control computer.Therefore, the laser beam guidance subsystem daemon waits untilcommunications have started. Furthermore, such communications can beprovided through the use of serial port communications.

Once laser connection is established, the laser beam guidance subsystemdaemon is commanded to initialize operations, which starts the compactlaser projection system operations, activates the laser chiller systemand reports the initial state of the laser. The laser chiller systembegins operation immediately but takes some time to properly chill thelaser head to operating temperatures. The robotic control system (100)waits until the laser temperature has stabilized before continuingoperations.

Once the laser is ready to be propagated, the robotic control systemoperations (described above) can start. The telescope (1) is pointed atan object. Then the laser beam guidance subsystem safety system checksif it is safe to propagate the laser at that time. If it is not, anotherobject is selected. Alternatively if it is safe, the laser beam guidancesubsystem is commanded to start. This command propagates the laserinside of the compact laser projection system (4). The laser safetyshutter is then opened which allows the laser to propagate out of thecompact laser projection system (4) and, for example, into the sky.

The laser beam is focused by the output lens (12) at a height of 10 kmabove the end of the telescope tube in the direction of the telescope(1). The laser beam is automatically positioned at the center range ofthe tip tilt mirror at the start of laser operation. This initialpositioning is performed by the AO system control anytime AO operationshas started or stopped.

The robotic control system (100) then takes a background image of the AOsystem. This background measures the laser background signal at acurrent position with any background due to objects. The robotic controlsystem (100) then sends the measurements through the laser beam guidancesubsystem daemon routine explained above. Once an appropriate alignmentis acquired, the laser beam is left in that position until the AO systemstarts operations. At that point, the tip tilt signal due to the lasermotions is measured by the WFS CCD and signals are sent by the AO systemto keep the laser in position.

The above process is continued until the present observation iscomplete, at which point the laser beam guidance subsystem daemon iscommanded to stop propagation of the laser beam from the compact laserprojection system and the laser safety shutter closed. If there is anerror during operations, the laser beam guidance subsystem isautomatically stopped, the safety shutter closed and a signal sent tothe robotic control system (100). The robotic control system (100) wouldthen stop the current scientific observation and attempt to fix theproblem and move to another observation.

The observing procedure continues, going through other objects, untilthe end of the night or when all objects have been viewed. At thatpoint, the laser safety shutter is closed. The laser beam guidancesubsystem is then commanded to stop operations and then shut down. Oncelaser beam guidance subsystem shut down has been completed, the power tothe laser and laser chiller are turned off with the NPS. Furthermore,the laser beam guidance subsystem daemon is then shut down as well.

The above description pertaining to the operation of the laser beamguidance subsystem daemon, as shown in FIG. 18, corresponds to 214(starting the LGS system) and 218 (stopping the LGS system) of FIG. 16when incorporated into the overall Robo-AO system.

With reference again to FIG. 16, after the shutdown of the LGS system(218), the Robo-AO subsystems are commanded to shutdown (219). Thisoccurs, for example, at the end of the night, when all objects have beenobserved or if a system error forces a shutdown. Following the commandto shutdown (219), the Robo-AO ensures that all threads have been closedproperly (122) otherwise any active threads could hang the roboticsystem control (100) up.

The following morning after observation has been completed, housekeepingand archiving activities are done. Such activities are performed byseparate software not associated with the robotic control system (100).

The examples set forth above are provided to give those of ordinaryskill in the art a complete disclosure and description of how to makeand use the embodiments of the robotic adaptive optics laser system, andare not intended to limit the scope of what the inventors regard astheir disclosure. The skilled person may find other suitableimplementations of the presented embodiments.

Discussion will now proceed to FIG. 19 which shows a computer systemthat may be used in combination with the control software describedabove. It should be understood that certain elements may be additionallyincorporated into computer system (300) and that the figure only showscertain basic elements (illustrated in the form of functional blocks).These functional blocks include a processor (310), memory (320), and oneor more input and/or output (I/O) devices (360) (or peripherals) thatare communicatively coupled via a local interface (350). The localinterface (350) can be, for example, metal tracks on a printed circuitboard, or any other forms of wired, wireless, and/or optical connectionmedia. Furthermore, the local interface (350) is a symbolicrepresentation of several elements such as controllers, buffers(caches), drivers, repeaters, and receivers that are generally directedat providing address, control, and/or data connections between multipleelements.

The processor (310) is a hardware device for executing software, moreparticularly, software stored in memory (320). The processor (310) canbe any commercially available processor or a custom-built device.Examples of suitable commercially available microprocessors includeprocessors manufactured by companies such as Intel®, AMD®, andMotorola®.

The memory (320) can include any type of one or more volatile memoryelements (e.g., random access memory (RAM, such as DRAM, SRAM, SDRAM,etc.)) and nonvolatile memory elements (e.g., ROM, hard drive, tape,CDROM, etc.). The memory elements may incorporate electronic, magnetic,optical, and/or other types of storage technology. It must be understoodthat the memory (320) can be implemented as a single device or as anumber of devices arranged in a distributed structure, wherein variousmemory components are situated remote from one another, but eachaccessible, directly or indirectly, by the processor (310).

The software in memory (320) may include one or more separate programs,each of which comprises an ordered listing of executable instructionsfor implementing logical functions. In the example of FIG. 10, thesoftware in the memory (320) includes an executable program (340) thatcan be executed to launch the various subsystem daemons in accordancewith the present invention. Memory (320) further includes a suitableoperating system (OS) (330). The OS (330) can be an operating systemthat is used in various types of commercially-available devices such as,for example, a personal computer running a Windows® OS, an Apple®product running an Apple-related OS, or an Android OS running in a smartphone. The operating system (330) essentially controls the execution ofexecutable program (340) and also the execution of other computerprograms, such as those providing scheduling, input-output control, fileand data management, memory management, and communication control andrelated services.

Executable program (340) is a source program, executable program (objectcode), script, or any other entity comprising a set of instructions tobe executed in order to perform a functionality. When a source program,then the program may be translated via a compiler, assembler,interpreter, or the like, and may or may not also be included within thememory (320), so as to operate properly in connection with the OS (330).

The I/O devices (360) may include input devices, for example but notlimited to, a keyboard, mouse, scanner, microphone, etc. Furthermore,the I/O devices (360) may also include output devices, for example butnot limited to, a printer and/or a display. Finally, the I/O devices(36) may further include devices that communicate both inputs andoutputs, for instance but not limited to, a modulator/demodulator(modem; for accessing another device, system, or network), a radiofrequency (RF) or other transceiver, a telephonic interface, a bridge, arouter, etc.

If the computer system (300) is a PC, workstation, or the like, thesoftware in the memory (320) may further include a basic input outputsystem (BIOS) (omitted for simplicity). The BIOS is a set of essentialsoftware routines that initialize and test hardware at startup, startthe OS (330), and support the transfer of data among the hardwaredevices. The BIOS is stored in ROM so that the BIOS can be executed whenthe computer system (300) is activated.

When the computer system (300) is in operation, the processor (310) isconfigured to execute software stored within the memory (320), tocommunicate data to and from the memory (320), and to generally controloperations of the computer system (300) pursuant to the software. Thecontrol system and the OS (330), in whole or in part, but typically thelatter, are read by the processor (310), perhaps buffered within theprocessor (310), and then executed.

When the subsystem daemons are implemented, as is shown in FIG. 10, itshould be noted that they can be stored on any computer readable storagemedium for use by, or in connection with, any computer related system ormethod. In the context of this document, a computer readable storagemedium is an electronic, magnetic, optical, or other physical device ormeans that can contain or store a computer program for use by, or inconnection with, a computer related system or method.

The control system can be embodied in any computer-readable storagemedium for use by or in connection with an instruction execution system,apparatus, or device, such as a computer-based system,processor-containing system, or other system that can fetch theinstructions from the instruction execution system, apparatus, or deviceand execute the instructions. In the context of this document, a“computer-readable storage medium” can be any means that can store,communicate, propagate, or transport the program for use by or inconnection with the instruction execution system, apparatus, or device.The computer readable storage medium can be, for example but not limitedto, an electronic, magnetic, optical, electromagnetic, infrared, orsemiconductor system, apparatus, or device. More specific examples (anon-exhaustive list) of the computer-readable storage medium wouldinclude the following: a portable computer diskette, a random accessmemory (RAM), a read-only memory (ROM), an erasable programmableread-only memory (EPROM, EEPROM, or Flash memory) an optical disk suchas a DVD or a CD.

In an alternative embodiment, where the control system is implemented inhardware, the audio data spread spectrum embedding and detection systemcan implemented with any one, or a combination, of the followingtechnologies, which are each well known in the art: a discrete logiccircuit(s) having logic gates for implementing logic functions upon datasignals, an application specific integrated circuit (ASIC) havingappropriate combinational logic gates, a programmable gate array(s)(PGA), a field programmable gate array (FPGA), etc.

Modifications of the above-described modes for carrying out the methodsand systems herein disclosed that are obvious to persons of skill in theart are intended to be within the scope of the following claims. Allpatents and publications mentioned in the specification are indicativeof the levels of skill of those skilled in the art to which thedisclosure pertains. All references cited in this disclosure areincorporated by reference to the same extent as if each reference hadbeen incorporated by reference in its entirety individually.

It is to be understood that the disclosure is not limited to particularmethods or systems, which can, of course, vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting. As used in this specification and the appended claims, thesingular forms “a”, “an”, and “the” include plural referents unless thecontent clearly dictates otherwise. The term “plurality” includes two ormore referents unless the content clearly dictates otherwise. Unlessdefined otherwise, all technical and scientific terms used herein havethe same meaning as commonly understood by one of ordinary skill in theart to which the disclosure pertains.

A number of embodiments of the disclosure have been described.Nevertheless, it will be understood that various modifications can bemade without departing from the spirit and scope of the presentdisclosure. Accordingly, other embodiments are within the scope of thefollowing claims.

The invention claimed is:
 1. A method comprising: activating a laserprojection system to propagate a laser beam, whereby at least a portionof the laser beam is returned to the system for detection of an error;configuring an adaptive optics system to detect the detected error toperform a compensating action comprising modifying an operatingcharacteristic of at least one optical component contained in the laserprojection system; and executing a computer-controlled automatedacquisition procedure to automatically align the laser projectionsystem, the automated acquisition procedure comprising: capturing in awavefront sensor, an image associated with a portion of the projectedlaser beam returned; using information obtained by processing thecaptured image to perform a compensating operation directed ataddressing the error; and executing an iterative routine that comprises:a) processing the image captured in the wavefront sensor to determine ifan overall brightness level in the captured image exceeds an acquisitionthreshold; b) when below the acquisition threshold, changing at leastone of an orientation or a curvature of a reflecting surface of thelaser steering mirror; and c) repeating steps a) and b) and when equalto or exceeding the acquisition threshold, terminating the iterativeroutine.
 2. The method of claim 1, wherein the error is a measureddistortion of the laser beam being returned to the system, the measureddistortion induced by the atmosphere.
 3. The method of claim 1, whereinthe automated acquisition procedure comprises an initializationprocedure that includes placing a laser steering mirror in a defaultorientation.
 4. The method of claim 1, further comprising: providing atelescope configured to observe one or more objects, the telescope beingassociated with the laser projection system whereby the laser projectionsystem projects a laser beam substantially parallel to a viewing axis ofthe telescope and the adaptive optics system whereby the adaptive opticssystem provides corrections to the telescope for distortion caused bythe atmosphere based on a measured distortion obtained from a portion ofthe laser beam returned by the atmosphere by modifying an operatingcharacteristic of at least one optical component contained in at leastone of the telescope or the laser projection system.
 5. The method ofclaim 1, wherein the telescope is also controllable by the automatedlaser alignment system.
 6. The method of claim 1, wherein the one ormore objects observed by the telescope are astronomical objects.
 7. Themethod of claim 1, wherein modifying the operating characteristic of atleast one optical component comprises operating a motor to modify atleast one of an orientation of a principal axis of a mirror or acurvature of a surface of the mirror.
 8. The method of claim 1, whereindetermining if the overall brightness level in the image exceeds theacquisition threshold comprises: dividing the processed image into aplurality of segments, each segment forming a corresponding image;measuring a brightness level of each image corresponding to theplurality of segments.
 9. The method of claim 8, further comprising:determining a total count of segments each having a segment brightnesslevel exceeding a threshold segment brightness level.
 10. The method ofclaim 9, further comprising: using the total count of segments as aparameter to determine if the overall brightness level in the capturedimage exceeds the acquisition threshold.
 11. The method of claim 1,wherein changing the at least one of an orientation or a curvature of areflecting surface of the laser steering mirror comprises moving thelaser steering mirror in an outward spiraling pattern.
 12. The method ofclaim 1, wherein the automated acquisition procedure comprises a firstacquisition procedure that provides for a coarse level of alignment tothe telescope followed by a second acquisition procedure that providesfor a fine level of alignment to the telescope.
 13. The method of claim1, further comprising first checking for a safe operation state beforeactivating the laser projection system.
 14. The method of claim 1,further comprising repetition of the activating and executing stepsuntil all objects are observed or a specified time has elapsed.